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← JEE Main 2014 · 9 Apr · Shift 1
MathematicsSingle correct+4 / -1Question 77 of 90

JEE Main 2014 · 9 Apr · Shift 1, Mathematics question 77

Let A={(x,y):y2≤4x, y−2x≥−4}A=\left\{(x,y):y^2\le4x,\ y-2x\ge-4\right\}. The area (in square units) of the region A is :

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Answer and worked solution

Official answer: B

The parabola y2=4xy^2=4x meets the line x=y+42x=\frac{y+4}2 where y2=2y+8y^2=2y+8, i.e. y=−2y=-2 and y=4y=4. The region lies between them:
∫−24(y+42−y24)dy=[y24+2y−y312]−24=203+73=9.\int_{-2}^{4}\left(\frac{y+4}2-\frac{y^2}4\right)dy=\left[\frac{y^2}4+2y-\frac{y^3}{12}\right]_{-2}^{4}=\frac{20}3+\frac73=9.