The area (in sq. units) of the region A={(x,y)∈R×R∣0≤x≤3,0≤y≤4,y≤x2+3x} is:
(A)326
(B)659✓ Correct
(C)653
(D)8
Answer: (B)
Solution
The region lies under the parabola y=x2+3x but is capped at y=4, so find where the curve reaches the cap: x2+3x=4 gives x=1. For 0≤x≤1 the parabola is the ceiling, while for 1≤x≤3 the flat line y=4 is. The area is ∫01(x2+3x)dx+∫134dx=[3x3+23x2]01+4(2)=(31+23)+8=611+8=659.
JEE Main · 2019 · 08 Apr 2019 · Shift 1 · Single correct option