Let Δ be the area of the region {(x,y)∈R2:x2+y2≤21,y2≤4x,x≥1}. Then 21(Δ−21sin−172) is equal to
(A)23−31
(B)3−32
(C)23−32
(D)3−34✓ Correct
Answer: (D)
Solution
The region lies inside x2+y2=21, inside the parabola y2=4x, with x≥1; the parabola meets the circle where x2+4x=21, at x=3 (with y=±23). By symmetry in the x-axis,