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CBSE - Class 9 Mathematics Linear Equations in Two Variables Worksheet

EXERCISE 4.2

1.
Find the value of $k$, if $x = 2$, $y = 1$ is a solution of the equation $2x + 3y = k$.
2.
Write four solutions for each of the following equations:
(iii) $x = 4y$
3.
Write four solutions for each of the following equations:
(ii) $\pi x + y = 9$
4.
Check which of the following are solutions of the equation $x - 2y = 4$ and which are not:
(i) $(0, 2)$
5.
Check which of the following are solutions of the equation $x - 2y = 4$ and which are not:
(iii) $(4, 0)$
6.
Check which of the following are solutions of the equation $x - 2y = 4$ and which are not:
(ii) $(2, 0)$
7.
Check which of the following are solutions of the equation $x - 2y = 4$ and which are not:
(v) $(1, 1)$
8.

Which one of the following options is true, and why? $y = 3x + 5$ has

a.

a unique solution

b.

only two solutions

c.

infinitely many solutions

9.
Check which of the following are solutions of the equation $x - 2y = 4$ and which are not:
(iv) $(\sqrt{2}, 4\sqrt{2})$
10.
Write four solutions for each of the following equations:
(i) $2x + y = 7$

Worksheet Answers

Solution:

Initial Setup & Theoretical Foundation

We are given the linear equation in two variables:

$x = 4y$

[Per the fundamental theorem of linear algebra], a linear equation in two variables of the form $ax + by + c = 0$ has infinitely many solutions. This is because for every arbitrary real value assigned to the independent variable, there exists a unique corresponding real value for the dependent variable. To find four distinct solutions, we will systematically assign four different real values to $y$ and solve for the corresponding values of $x$.

Step 1: Deriving the First Solution

Let us assign the value $y = 0$. Substituting this into the given equation:

$x = 4(0)$

$x = 0$

Thus, the first ordered pair $(x, y)$ that satisfies the equation is $(0, 0)$.

Step 2: Deriving the Second Solution

Let us assign the value $y = 1$. Substituting this into the given equation:

$x = 4(1)$

$x = 4$

Thus, the second ordered pair $(x, y)$ that satisfies the equation is $(4, 1)$.

Step 3: Deriving the Third Solution

Let us assign the value $y = 2$. Substituting this into the given equation:

$x = 4(2)$

$x = 8$

Thus, the third ordered pair $(x, y)$ that satisfies the equation is $(8, 2)$.

Step 4: Deriving the Fourth Solution

Let us assign a negative integer to demonstrate solutions in the third quadrant. Let $y = -1$. Substituting this into the given equation:

$x = 4(-1)$

$x = -4$

Thus, the fourth ordered pair $(x, y)$ that satisfies the equation is $(-4, -1)$.

Tabular Representation of Solutions

We can organize the derived solutions into a coordinate table to clearly map the relationship between $x$ and $y$.

Solution Number Value of $y$ Calculated Value of $x$ ($x = 4y$) Ordered Pair $(x, y)$
1 $0$ $0$ $(0, 0)$
2 $1$ $4$ $(4, 1)$
3 $2$ $8$ $(8, 2)$
4 $-1$ $-4$ $(-4, -1)$

Graphical Verification

Plotting these points on a Cartesian plane confirms that they are collinear, forming the straight line defined by $x = 4y$.

X Y 0 x = 4y (0, 0) (4, 1) (8, 2) (-4, -1)

Final Solution: Four valid solutions for the equation $x = 4y$ are $(0, 0)$, $(4, 1)$, $(8, 2)$, and $(-4, -1)$.

Solution:

Initial Setup & Algebraic Formulation

We are tasked with finding four distinct solutions for the following linear equation in two variables:

$\pi x + y = 9$

A linear equation in two variables has infinitely many solutions. A solution is defined as an ordered pair $(x, y)$ that satisfies the equation. To systematically generate these solutions, we will express one variable in terms of the other.

Step 1: Isolating the Dependent Variable

To make the calculation of ordered pairs straightforward, we isolate the dependent variable ($y$) in terms of the independent variable ($x$). [Per the Subtraction Property of Equality, subtracting $\pi x$ from both sides of the equation yields:]

$y = 9 - \pi x$

We can now substitute arbitrary real numbers for $x$ to compute the corresponding exact values of $y$.

Step 2: Deriving the First Solution

Let us assign $x = 0$. Substituting this value into our isolated equation:

$y = 9 - \pi(0)$

$y = 9 - 0$

$y = 9$

Thus, the first solution is the ordered pair $(0, 9)$. [This point also represents the y-intercept of the linear graph].

Step 3: Deriving the Second Solution

Let us assign $x = 1$. Substituting this value into the equation:

$y = 9 - \pi(1)$

$y = 9 - \pi$

Thus, the second solution is the ordered pair $(1, 9 - \pi)$.

Step 4: Deriving the Third Solution

Let us assign $x = 2$. Substituting this value into the equation:

$y = 9 - \pi(2)$

$y = 9 - 2\pi$

Thus, the third solution is the ordered pair $(2, 9 - 2\pi)$.

Step 5: Deriving the Fourth Solution

Let us assign $x = -1$. Substituting this value into the equation:

$y = 9 - \pi(-1)$

$y = 9 + \pi$

Thus, the fourth solution is the ordered pair $(-1, 9 + \pi)$.

Step 6: Tabular Summary of Solutions

We can organize the derived solutions into a Cartesian coordinate table. This demonstrates the linear relationship and prepares the data for graphical representation.

Independent Variable ($x$) Dependent Variable ($y$) Ordered Pair $(x, y)$
$0$ $9$ $(0, 9)$
$1$ $9 - \pi$ $(1, 9 - \pi)$
$2$ $9 - 2\pi$ $(2, 9 - 2\pi)$
$-1$ $9 + \pi$ $(-1, 9 + \pi)$

Step 7: Graphical Representation of the Linear Equation

Below is the geometric interpretation of the equation $\pi x + y = 9$ plotted on a Cartesian plane. The line represents the locus of all infinite solutions, with our four specific calculated points highlighted. (Note: For spatial plotting purposes, $\pi$ is approximated as $3.14$).

x y 0 1 2 -1 9 (0, 9) (1, 9-π) (2, 9-2π) (-1, 9+π) πx + y = 9

Final Solution: Four valid solutions for the equation $\pi x + y = 9$ are $(0, 9)$, $(1, 9 - \pi)$, $(2, 9 - 2\pi)$, and $(-1, 9 + \pi)$.

Solution:

Step 1: Initial Setup & Given Variables

We are given the linear equation in two variables:

$x - 2y = 4$

We need to determine whether the coordinate point $(0, 2)$ is a valid solution to this equation. In the Cartesian coordinate system, an ordered pair $(x, y)$ represents a solution to an equation if and only if substituting the $x$ and $y$ values into the equation results in a true mathematical statement [Per the Fundamental Principle of Algebraic Substitution].

  • Given $x$-coordinate (abscissa): $x = 0$
  • Given $y$-coordinate (ordinate): $y = 2$

Step 2: Substitution into the Left-Hand Side (LHS)

We isolate the Left-Hand Side (LHS) of the given equation and substitute the given coordinates:

$\text{LHS} = x - 2y$

Substituting $x = 0$ and $y = 2$:

$\text{LHS} = (0) - 2(2)$

$\text{LHS} = 0 - 4$

$\text{LHS} = -4$

Step 3: Comparison with the Right-Hand Side (RHS)

The Right-Hand Side (RHS) of the original equation is a constant:

$\text{RHS} = 4$

Comparing the evaluated LHS with the RHS:

$-4 \neq 4$

$\text{LHS} \neq \text{RHS}$

Because the substitution yields an inequality, the ordered pair $(0, 2)$ does not satisfy the equation.

Step 4: Geometric Interpretation & Verification

Geometrically, a linear equation in two variables represents a straight line on a Cartesian plane. Every point that lies exactly on this line is a solution to the equation. Since $(0, 2)$ does not satisfy the algebraic equation, the point $(0, 2)$ will not lie on the line $x - 2y = 4$.

To graph the line $x - 2y = 4$, we find its intercepts:

  • x-intercept (set $y = 0$): $x - 2(0) = 4 \implies x = 4$. Point: $(4, 0)$
  • y-intercept (set $x = 0$): $0 - 2y = 4 \implies y = -2$. Point: $(0, -2)$

The visual representation below proves that the point $(0, 2)$ is spatially disconnected from the solution set (the line).

X Y 0 x - 2y = 4 (4, 0) (0, -2) (0, 2)

Final Solution: Since substituting $x = 0$ and $y = 2$ results in $\text{LHS} \neq \text{RHS}$ ($-4 \neq 4$), the point $(0, 2)$ is NOT a solution to the equation $x - 2y = 4$.

Solution:

Given Variables & Initial Setup

We are given a linear equation in two variables and an ordered pair representing a point on the Cartesian plane. Our objective is to determine mathematically whether the given point lies on the line defined by the equation.

  • The Linear Equation: $x - 2y = 4$
  • The Ordered Pair (Point): $(4, 0)$

Step 1: Coordinate Identification & Substitution

An ordered pair is written in the format $(x, y)$. [Per the fundamental principles of coordinate geometry, a point is a solution to an equation if and only if substituting its coordinates into the equation results in a true mathematical statement].

From the given point $(4, 0)$, we extract the specific coordinate values:

  • Abscissa ($x$-coordinate): $x = 4$
  • Ordinate ($y$-coordinate): $y = 0$

We substitute these values into the Left-Hand Side (LHS) of the given equation.

$\text{LHS} = x - 2y$

$\text{LHS} = (4) - 2(0)$

Step 2: Algebraic Evaluation

Applying the standard order of operations (PEMDAS/BODMAS), we first perform the multiplication, followed by the subtraction.

$\text{LHS} = 4 - 0$

$\text{LHS} = 4$

Step 3: Verification of Equality

We now compare the evaluated Left-Hand Side (LHS) with the Right-Hand Side (RHS) of the original equation.

  • $\text{LHS} = 4$
  • $\text{RHS} = 4$

Since $\text{LHS} = \text{RHS}$, the equation holds true. [By the Axiom of Equality, the substitution satisfies the linear equation, proving that the point geometrically lies exactly on the line].

Graphical Representation & Verification

To rigorously verify this result, we can map the equation $x - 2y = 4$ and the point $(4, 0)$ onto a Cartesian coordinate system. The line intersects the x-axis precisely at the point $(4, 0)$.

X Y 0 4 -4 4 -2 x - 2y = 4 (4, 0)

Final Solution: The ordered pair $(4, 0)$ satisfies the equation $x - 2y = 4$. Therefore, $(4, 0)$ is a valid solution to the given linear equation.

Solution:

Given Variables & Initial Setup

We are tasked with determining whether the specific coordinate pair is a valid solution to the given linear equation in two variables.

  • The Linear Equation: $x - 2y = 4$
  • The Coordinate Pair to Test: $(2, 0)$

[Theoretical Foundation: A coordinate pair $(x, y)$ is considered a solution to a linear equation if and only if substituting the $x$ and $y$ values into the equation yields a true mathematical statement. This requires the Left-Hand Side (LHS) of the equation to perfectly equal the Right-Hand Side (RHS) after evaluation.]

Step 1: Isolate the Left-Hand Side (LHS) and Right-Hand Side (RHS)

From the given equation $x - 2y = 4$, we separate the expression into two distinct sides for independent evaluation:

  • LHS: $x - 2y$
  • RHS: $4$

Step 2: Substitution of the Coordinate Values

The given point is $(2, 0)$. In the Cartesian coordinate system, an ordered pair is formatted as $(x, y)$. Therefore, we extract the following values:

  • $x = 2$
  • $y = 0$

We substitute these specific values into the LHS expression:

$\text{LHS} = (2) - 2(0)$

Step 3: Algebraic Evaluation

Perform the arithmetic operations according to the standard order of operations (PEMDAS/BODMAS):

$\text{LHS} = 2 - 0$

$\text{LHS} = 2$

Step 4: Comparison and Logical Conclusion

Now, we compare the evaluated LHS with the constant RHS:

  • $\text{LHS} = 2$
  • $\text{RHS} = 4$

Since $2 \neq 4$, we conclude that $\text{LHS} \neq \text{RHS}$.

[Geometrical Interpretation: Because the equation is not satisfied, the point $(2, 0)$ does not lie on the straight line represented by the equation $x - 2y = 4$.]

Visual Verification: Graphical Representation

Below is the precise Cartesian plot of the line $x - 2y = 4$ alongside the tested point $(2, 0)$. Notice that the line intersects the x-axis at $(4, 0)$, leaving the point $(2, 0)$ distinctly off the line.

X Y 0 x - 2y = 4 (4, 0) (2, 0) Tested Point

Final Solution: Since the substitution of $x = 2$ and $y = 0$ results in $2 \neq 4$, the coordinate pair $(2, 0)$ is NOT a solution to the equation $x - 2y = 4$.

Solution:

Given Variables & Initial Setup

We are tasked with determining whether the coordinate point $(1, 1)$ is a valid solution to the given linear equation in two variables. The foundational elements of our analysis are:

  • The Linear Equation: $x - 2y = 4$
  • The Test Coordinate: $(1, 1)$

Step 1: Deconstructing the Coordinate Pair

In the Cartesian coordinate system, an ordered pair is universally represented in the format $(x, y)$. [By the fundamental axiom of coordinate geometry], the first value corresponds to the abscissa (the $x$-coordinate) and the second value corresponds to the ordinate (the $y$-coordinate).

Extracting the values from our test coordinate $(1, 1)$:

  • $x = 1$
  • $y = 1$

Step 2: Substitution into the Left-Hand Side (LHS)

To verify if the point lies on the line defined by the equation, we must substitute the extracted $x$ and $y$ values into the Left-Hand Side (LHS) of the equation. [Per the algebraic property of substitution, a point is a solution if and only if it satisfies the equality].

The LHS of the equation is given by:

$\text{LHS} = x - 2y$

Substituting $x = 1$ and $y = 1$:

$\text{LHS} = (1) - 2(1)$

$\text{LHS} = 1 - 2$

$\text{LHS} = -1$

Step 3: Comparative Analysis of LHS and RHS

We now compare our evaluated LHS with the Right-Hand Side (RHS) of the original equation.

  • $\text{LHS} = -1$
  • $\text{RHS} = 4$

Comparing the two values:

$-1 \neq 4$

Since the Left-Hand Side does not equal the Right-Hand Side ($\text{LHS} \neq \text{RHS}$), the coordinate pair $(1, 1)$ fails to satisfy the linear equation.

Step 4: Graphical Verification

To provide rigorous geometric proof, we can visualize the linear equation $x - 2y = 4$ and the point $(1, 1)$ on a Cartesian plane. A point is a solution to an equation if and only if it lies exactly on the line representing that equation.

x y O 1 4 1 -2 x - 2y = 4 (4, 0) (0, -2) (1, 1)

As demonstrated in the high-precision graph above, the blue line represents the infinite set of solutions for $x - 2y = 4$. The red point representing the coordinate $(1, 1)$ clearly lies outside the trajectory of the line, confirming our algebraic derivation geometrically.

Final Conclusion

Because the substitution of $x = 1$ and $y = 1$ results in a mathematical contradiction ($-1 \neq 4$), the point does not satisfy the equation.

Final Solution: The coordinate $(1, 1)$ is not a solution to the equation $x - 2y = 4$.

8.

Solution:

Initial Setup & Theoretical Foundation

The given mathematical statement is the equation $y = 3x + 5$. This is a linear equation in two variables, $x$ and $y$. The standard form of a linear equation in two variables is $ax + by + c = 0$. By rearranging the given equation, we obtain $-3x + y - 5 = 0$, where the coefficients are $a = -3$, $b = 1$, and the constant term is $c = -5$.

The standard options for this classical problem are:

  • (i) A unique solution
  • (ii) Only two solutions
  • (iii) Infinitely many solutions

Step 1: Algebraic Analysis of Solutions

A "solution" to a linear equation in two variables is defined as an ordered pair $(x, y)$ that satisfies the equation. In the equation $y = 3x + 5$, $x$ acts as the independent variable and $y$ acts as the dependent variable.

[Per the fundamental properties of real numbers], for every distinct real value assigned to $x$, there exists a corresponding unique real value for $y$. Let us systematically substitute arbitrary real numbers for $x$ to observe the resulting values of $y$:

Independent Variable ($x$) Substitution Process ($y = 3x + 5$) Dependent Variable ($y$) Solution Coordinate $(x, y)$
$0$ $y = 3(0) + 5 = 0 + 5$ $5$ $(0, 5)$
$1$ $y = 3(1) + 5 = 3 + 5$ $8$ $(1, 8)$
$-1$ $y = 3(-1) + 5 = -3 + 5$ $2$ $(-1, 2)$
$-2$ $y = 3(-2) + 5 = -6 + 5$ $-1$ $(-2, -1)$
$\frac{1}{3}$ $y = 3(\frac{1}{3}) + 5 = 1 + 5$ $6$ $(\frac{1}{3}, 6)$

Because the set of real numbers ($\mathbb{R}$) is infinite, we can choose infinitely many values for $x$. Consequently, we will generate infinitely many corresponding values for $y$. Therefore, the equation possesses infinitely many solutions.

Step 2: Geometric Interpretation

[By the geometric definition of linear equations], any linear equation in two variables represents a straight line on a two-dimensional Cartesian coordinate system. Every single point that lies on this line represents a valid solution $(x, y)$ to the equation.

A straight line extends indefinitely in both directions. Since a line is composed of an infinite number of points, the equation representing that line must inherently have an infinite number of solutions.

Step 3: Visual Proof via Cartesian Mapping

Below is the precise geometric representation of the equation $y = 3x + 5$. The red coordinates highlight specific solutions, demonstrating that the line passes through an infinite continuum of points.

X X' Y Y' O (0,0) y = 3x + 5 (0, 5) (-1, 2) (-2, -1) (-3, -4)

Logical Deduction

Based on both the algebraic substitution method and the geometric mapping, it is evident that the relationship $y = 3x + 5$ is not restricted to one or two specific coordinate pairs. The equation acts as a continuous function mapping the domain of all real numbers to a range of all real numbers.

Final Solution: The true option is "Infinitely many solutions". This is because for every real value of $x$, there is a corresponding unique real value of $y$, and geometrically, the equation represents a straight line composed of an infinite number of points.

Solution:

Initial Setup & Given Variables

We are tasked with verifying whether the coordinate pair $(\sqrt{2}, 4\sqrt{2})$ satisfies the given linear equation in two variables. The foundational components of our analysis are:

  • The Linear Equation: $x - 2y = 4$
  • The Ordered Pair: $(x, y) = (\sqrt{2}, 4\sqrt{2})$

[Per the fundamental theorem of algebra and coordinate geometry, an ordered pair $(x, y)$ is a valid solution to an equation if and only if substituting the values of $x$ and $y$ into the equation results in a true mathematical statement where the Left Hand Side (LHS) equals the Right Hand Side (RHS)].

Step 1: Substitution of Coordinates

We isolate the Left Hand Side (LHS) of the equation and substitute the specific values from the ordered pair.

Given LHS: $x - 2y$

Substitute $x = \sqrt{2}$ and $y = 4\sqrt{2}$:

$\text{LHS} = (\sqrt{2}) - 2(4\sqrt{2})$

Step 2: Algebraic Evaluation

Next, we simplify the expression using the properties of real numbers and radical arithmetic.

Multiply the constant $2$ by the coefficient of the radical term $4\sqrt{2}$ [By the associative property of multiplication]:

$\text{LHS} = \sqrt{2} - 8\sqrt{2}$

Factor out the common radical term $\sqrt{2}$ [By the distributive property of multiplication over addition/subtraction]:

$\text{LHS} = (1 - 8)\sqrt{2}$

$\text{LHS} = -7\sqrt{2}$

Step 3: Comparison with Right Hand Side (RHS)

We now compare the evaluated LHS with the constant RHS of the original equation.

Left Hand Side (LHS) Right Hand Side (RHS) Logical Relation
$-7\sqrt{2}$ $4$ $\text{LHS} \neq \text{RHS}$

Since $-7\sqrt{2}$ is an irrational number approximately equal to $-9.899$, and the RHS is the rational integer $4$, the two sides are strictly unequal.

Geometric Verification

Geometrically, the equation $x - 2y = 4$ represents a straight line on the Cartesian plane. If the point $(\sqrt{2}, 4\sqrt{2})$ were a solution, it would lie exactly on this line. The precise SVG rendering below demonstrates the spatial divergence between the line and the coordinate point.

X Y 0 x - 2y = 4 (√2, 4√2)

Figure 1: The point $(\sqrt{2}, 4\sqrt{2})$ clearly does not intersect the line $x - 2y = 4$.

Final Solution: Since substituting $x = \sqrt{2}$ and $y = 4\sqrt{2}$ yields $-7\sqrt{2} \neq 4$, the ordered pair $(\sqrt{2}, 4\sqrt{2})$ is NOT a solution to the equation $x - 2y = 4$.

Solution:

Initial Setup & Algebraic Isolation

We are given the linear equation in two variables:

$2x + y = 7$

To systematically find solutions for this equation, it is mathematically highly efficient to express one variable in terms of the other. We will isolate the dependent variable $y$ on the left side of the equation [Per the fundamental properties of equality, by subtracting $2x$ from both sides].

$y = 7 - 2x$

A "solution" to a linear equation in two variables is an ordered pair $(x, y)$ that satisfies the equation. Since this is a linear equation defined over the set of real numbers ($\mathbb{R}$), it possesses infinitely many solutions. We will select four arbitrary integer values for the independent variable $x$ to compute the corresponding values of $y$.

Step 1: Calculating the First Solution

Let us assign the value $x = 0$. Substituting this into our isolated equation:

$y = 7 - 2(0)$

$y = 7 - 0$

$y = 7$

This yields our first ordered pair: $(0, 7)$.

Step 2: Calculating the Second Solution

Let us assign the value $x = 1$. Substituting this into the equation:

$y = 7 - 2(1)$

$y = 7 - 2$

$y = 5$

This yields our second ordered pair: $(1, 5)$.

Step 3: Calculating the Third Solution

Let us assign the value $x = 2$. Substituting this into the equation:

$y = 7 - 2(2)$

$y = 7 - 4$

$y = 3$

This yields our third ordered pair: $(2, 3)$.

Step 4: Calculating the Fourth Solution

Let us assign the value $x = 3$. Substituting this into the equation:

$y = 7 - 2(3)$

$y = 7 - 6$

$y = 1$

This yields our fourth ordered pair: $(3, 1)$.

Tabular Representation of Solutions

We can organize the derived coordinates into a data table to clearly demonstrate the linear relationship between $x$ and $y$. Notice that for every $1$ unit increase in $x$, $y$ decreases by $2$ units [This represents the slope of the line, $m = -2$].

Independent Variable ($x$) Dependent Variable ($y$) Ordered Pair $(x, y)$
$0$ $7$ $(0, 7)$
$1$ $5$ $(1, 5)$
$2$ $3$ $(2, 3)$
$3$ $1$ $(3, 1)$

Graphical Representation (Cartesian Plane)

Plotting these four points on a Cartesian coordinate system verifies that they are collinear, forming the straight line defined by $2x + y = 7$.

X Y 0 1 2 3 4 1 3 5 7 2x + y = 7 (0, 7) (1, 5) (2, 3) (3, 1)

Final Solution: Four distinct solutions for the linear equation $2x + y = 7$ are $(0, 7)$, $(1, 5)$, $(2, 3)$, and $(3, 1)$.

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