If the area of the region \(x, y) : 1 + x2 y \x + 7, 11 - 3x\\ is A, then 3A is equal to :
- 50
- 46
- 49
- 47
Answer
(1) 50
Solution
Lines y = x + 7 and y = 11 - 3x meet at (1, 8); for x 1 the smaller one is x + 7, for x 1 it is 11 - 3x.
1 + x2 = x + 7 x2 - x - 6 = 0 x = -2 (also 3, outside the region)
1 + x2 = 11 - 3x x2 + 3x - 10 = 0 x = 2 (also −5, outside the region)
[figure]
A = -21 (x + 7 - 1 - x2) dx + 12 (11 - 3x - 1 - x2) dx
= [6x + x22 - x33 ]-21 + [10x - 3x22 - x33 ]12
= ( 376 + 223 ) + ( 343 - 496 )
= 272 + 196 = 503
3A = 50
Answer: (1)