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Q2:
Solve the following Linear Programming Problems graphically:
2. Minimise $Z = – 3x + 4y$ subject to $x + 2y \leq 8$, $3x + 2y \leq 12$, $x \geq 0$, $y \geq 0$.
Solution :
Step 1: Establishing Constraints and Feasible Region
We are given the objective function $Z = -3x + 4y$ which is to be minimized, subject to the following system of linear inequalities:
- $x + 2y \leq 8$ [Constraint 1]
- $3x + 2y \leq 12$ [Constraint 2]
- $x \geq 0, y \geq 0$ [Non-negativity constraints]
Step 2: Identifying Boundary Lines
To determine the feasible region, we solve for the boundary lines by converting inequalities to equalities:
- Line 1: $x + 2y = 8$. Intercepts: $(8, 0)$ and $(0, 4)$.
- Line 2: $3x + 2y = 12$. Intercepts: $(4, 0)$ and $(0, 6)$.
Step 3: Determining the Intersection Point
Solving the system of linear equations to find the vertex where the two constraint lines meet:
$x + 2y = 8$ ... (Eq. i)
$3x + 2y = 12$ ... (Eq. ii)
Subtracting (Eq. i) from (Eq. ii): $(3x - x) + (2y - 2y) = 12 - 8 \implies 2x = 4 \implies x = 2$.
Substituting $x = 2$ into (Eq. i): $2 + 2y = 8 \implies 2y = 6 \implies y = 3$.
The point of intersection is $(2, 3)$.
Step 4: Evaluating the Objective Function at Vertices
The feasible region is bounded by the vertices $(0, 0)$, $(4, 0)$, $(2, 3)$, and $(0, 4)$. We evaluate $Z = -3x + 4y$ at each point:
| Corner Point $(x, y)$ | $Z = -3x + 4y$ |
|---|---|
| $(0, 0)$ | $-3(0) + 4(0) = 0$ |
| $(4, 0)$ | $-3(4) + 4(0) = -12$ |
| $(2, 3)$ | $-3(2) + 4(3) = -6 + 12 = 6$ |
| $(0, 4)$ | $-3(0) + 4(4) = 16$ |
Step 5: Determining the Minimum Value
Comparing the values obtained: $0, -12, 6, 16$. The minimum value is $-12$, which occurs at the point $(4, 0)$. [Per the Corner Point Theorem for Linear Programming].
Final Solution: The minimum value of $Z$ is $-12$ at the point $(4, 0)$.
More Questions from Class 12 Mathematics Linear Programming EXERCISE 12.1
- Q1: Solve the following Linear Programming Problems graphically: 1. Maximise $Z = 3x + 4y$ subject to the constraints : $x + y \leq 4$, $x \geq 0$, $y \geq 0$.
- Q3: Solve the following Linear Programming Problems graphically: 3. Maximise $Z = 5x + 3y$ subject to $3x + 5y \leq 15$, $5x + 2y \leq 10$, $x \geq 0$, $y \geq 0$.
- Q4: Solve the following Linear Programming Problems graphically: 4. Minimise $Z = 3x + 5y$ such that $x + 3y \geq 3$, $x + y \geq 2$, $x, y \geq 0$.
- Q5: Solve the following Linear Programming Problems graphically: 5. Maximise $Z = 3x + 2y$ subject to $x + 2y \leq 10$, $3x + y \leq 15$, $x, y \geq 0$.
- Q6: Solve the following Linear Programming Problems graphically: 6. Minimise $Z = x + 2y$ subject to $2x + y \geq 3$, $x + 2y \geq 6$, $x, y \geq 0$. Show that the minimum of $Z$ occurs at more than two points.
- Q7: Solve the following Linear Programming Problems graphically: 7. Minimise and Maximise $Z = 5x + 10y$ subject to $x + 2y \leq 120$, $x + y \geq 60$, $x – 2y \geq 0$, $x, y \geq 0$.
- Q8: Solve the following Linear Programming Problems graphically: 8. Minimise and Maximise $Z = x + 2y$ subject to $x + 2y \geq 100$, $2x – y \leq 0$, $2x + y \leq 200$; $x, y \geq 0$.
- Q9: Solve the following Linear Programming Problems graphically: 9. Maximise $Z = – x + 2y$, subject to the constraints: $x \geq 3$, $x + y \geq 5$, $x + 2y \geq 6$, $y \geq 0$.
- Q10: Solve the following Linear Programming Problems graphically: 10. Maximise $Z = x + y$, subject to $x – y \leq –1$, $–x + y \leq 0$, $x, y \geq 0$.
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