Area enclosed by lines and axes

CAT 2020 Slot 3 · QA · Medium · Coordinate geometry

The area, in sq. units, enclosed by the lines x=2x = 2, y=x2+4y = |x - 2| + 4, the X-axis and the Y-axis is equal to

  1. A.

    12

  2. B.

    8

  3. C.

    6

  4. D.

    10

Answer

D

Explanation

The region is bounded by: x=0x = 0 (Y-axis), x=2x = 2, y=0y = 0 (X-axis), y=x2+4y = |x - 2| + 4.

For x[0,2]x \in [0, 2], x20x - 2 \le 0, so x2=2x|x - 2| = 2 - x. Hence y=(2x)+4=6xy = (2 - x) + 4 = 6 - x.

The shape is a trapezium with vertices (0,0)(0,0), (2,0)(2,0), (2,4)(2,4), and (0,6)(0,6). Area = 02(6x)dx=[6xx22]02=122=10\int_{0}^{2} (6 - x) dx = \left[ 6x - \frac{x^2}{2} \right]_0^2 = 12 - 2 = 10.

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