Area of Region Defined by Inequalities

CAT 2019 Slot 1 · QA · Medium · Co-geometry

Let SS be the set of all points (x,y)(x, y) in the x-y plane such that x+y2|x| + |y| \le 2 and x1|x| \ge 1. Then, the area, in square units, of the region represented by SS equals

Answer

2

Explanation

x+y2|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. x1|x| \ge 1 restricts x1x \le -1 or x1x \ge 1. The region is composed of two symmetrical triangles on the left and right. In the first quadrant (x1x \ge 1): x+y2    y2xx + y \le 2 \implies y \le 2 - x. For x[1,2]x \in [1, 2], yy goes from 00 to 2x2-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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