Area of Region Defined by Inequalities

CAT 2019 Slot 1 · Quantitative Ability · Medium · Co-geometry

Let SS be the set of all points (x,y)(x, y) in the x-y plane such that ∣x∣+∣y∣≤2|x| + |y| \le 2 and ∣x∣≥1|x| \ge 1. Then, the area, in square units, of the region represented by SS equals

Answer

2

Explanation

∣x∣+∣y∣≤2|x| + |y| \le 2 forms a square with vertices at (2,0),(0,2),(−2,0),(0,−2)(2,0), (0,2), (-2,0), (0,-2), total area =8= 8. ∣x∣≥1|x| \ge 1 restricts x≤−1x \le -1 or x≥1x \ge 1. The region is composed of two symmetrical triangles on the left and right. In the first quadrant (x≥1x \ge 1): x+y≤2  ⟹  y≤2−xx + y \le 2 \implies y \le 2 - x. For x∈[1,2]x \in [1, 2], yy goes from 00 to 2−x2-x. This is a right triangle with base 11 and height 11, area =0.5= 0.5. By 4-fold symmetry across quadrants, total area =4×0.5=2= 4 \times 0.5 = 2.

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