NCERT Class XI Mathematics - Linear Inequalities - Solutions

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Question : 43
Total: 65
2x + y ≥ 8, x + 2y ≥ 10
Solution:  
The inequalities are 2x + y ≥ 8
and x + 2y ≥ 10
(i) Let us draw the graph of the line
l1 : 2x + y = 8 passes through (4, 0) and (0, 8) which is represented by AB.
Consider the inequality 2x + y ≥ 8

Putting x = y = 0, we get 0 ≥ 8, which is false.
∴ Origin does not lie in the region of 2x + y ≥ 8.
i.e., 2x + y ≥ 8 represents the area above the line AB and all the points lying on 2x + y = 8.
(ii) Let us draw the graph of line
l2 : x + 2y = 10, passes through (10, 0) and (0, 5) which is represented by CD. Consider the inequality x + 2y ≥ 10
Putting x = 0, y = 0, we have 0 ≥ 10, which is false.
∴ The origin does not lie in region of x + 2y ≥ 10
i.e., x + 2y ≥ 10 represents the area above the line CD and all the points lying on x + 2y = 10.
⇒ The common region of both the inequality is the shaded region as shown in the figure.
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