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Q2(i):
Evaluate the following products without multiplying directly: (i) $103 \times 107$

Solution :

Initial Setup & Algebraic Transformation

We are tasked with evaluating the numerical product $103 \times 107$ without executing direct multiplication. To achieve this, we must transform the arithmetic operation into an algebraic framework by expressing each factor as a binomial with a common base.

We decompose the given numbers using the base $100$:

  • $103 = 100 + 3$
  • $107 = 100 + 7$

Thus, the product can be rewritten as:

$103 \times 107 = (100 + 3)(100 + 7)$

Step 1: Selection of the Algebraic Identity

The expression $(100 + 3)(100 + 7)$ perfectly matches the standard polynomial identity for the product of two binomials sharing a common term. [Per the fundamental algebraic identity of binomial expansion]:

$(x + a)(x + b) = x^2 + (a + b)x + ab$

Step 2: Geometric Visualization of the Identity

To rigorously prove the spatial validity of this identity, we can represent the product as the area of a rectangle with dimensions $(x + a)$ and $(x + b)$. The total area is the sum of four distinct sub-rectangles.

x = 100 b = 7 x = 100 a = 3 x² = 10000 bx = 700 ax = 300 ab = 21

Step 3: Variable Assignment and Substitution

By mapping our specific numerical values to the variables in the identity, we establish the following parameters:

  • $x = 100$
  • $a = 3$
  • $b = 7$

Substituting these values into the identity $(x + a)(x + b) = x^2 + (a + b)x + ab$, we obtain:

$(100 + 3)(100 + 7) = (100)^2 + (3 + 7)(100) + (3 \times 7)$

Step 4: Algebraic Expansion and Arithmetic Computation

We now evaluate each term of the expanded polynomial sequentially [adhering to the standard order of operations, PEMDAS/BODMAS]:

  • First Term ($x^2$): $(100)^2 = 100 \times 100 = 10000$
  • Middle Term ($(a+b)x$): $(3 + 7) \times 100 = 10 \times 100 = 1000$
  • Last Term ($ab$): $3 \times 7 = 21$

Step 5: Final Summation

We synthesize the evaluated terms to find the total product:

$10000 + 1000 + 21$

$= 11000 + 21$

$= 11021$

Final Solution: The evaluated product of $103 \times 107$, derived using algebraic identities without direct multiplication, is $11021$.


More Questions from Class 9 Mathematics Polynomials EXERCISE 2.4


CBSE Solutions for Class 9 Mathematics Polynomials


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