NCERT Class XI Mathematics - Linear Inequalities - Solutions

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Question : 45
Total: 65
5x + 4y ≤ 20, x ≥ 1, y ≥ 2
Solution:  
The inequalities are 5x + 4y ≤ 20, x ≥ 1, y ≥ 2
(i) The line l1 : 5x + 4y = 20 passes through (4, 0) and (0, 5). This line is represented by AB.
Consider the inequality 5x + 4y ≤ 20
Putting x = 0, y = 0
0 + 0 = 0 ≤ 20, which is true.
The origin lies in this region, i.e., region below the line 5x + 4y = 20 and all the points lying on it belong to 5x + 4y ≤ 20.
(ii) The line l2 : y = 2, line is parallel to x-axis at a distance 2 from the origin.
It is represented by EF. Putting y = 0, 0 ≥ 2 is not true. Origin does not lie in this region.
Region above y = 2 represents the inequality y ≥ 2 including the points lying on it.
(iii) The line l3 : x = 1, line parallel to y-axis at a distance 1 from the origin.
It is represented by CD. Putting x = 0 in x – 1 ≥ 0
–1 ≥ 0, which is not true.
Origin does not lie in this region.
∴ The region on the right of x = 1 and all the points lying on it belong to x ≥ 1.

∴ Shaded area bounded by ΔPQR is the solution of given inequalities.
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