If the area of the region \(x, y) : 1 - 2x y 4 - x2, x 0, y 0\ is , , N, ( , ) = 1, then the value of ( + ) is:
- 73
- 85
- 67
- 91
Answer
(1) 73
Solution
Upper boundary y = 4 - x2 meets y = 0 at x = 2 (for x 0)
1 - 2x 4 - x2 ⇔ (x - 3)(x + 1) 0, true for all x [0, 2]
Lower boundary: y = 1 - 2x for 0 x 12 and y = 0 for 12 x 2
Area = 02 (4 - x2) dx - 01/2 (1 - 2x) dx
= (8 - 83 ) - ( 12 - 14 )
= 163 - 14 = 6112
= 61, = 12
+ = 73
Answer: (1)