Let the domain of the function f(x) = 3 5 (7 - 2 (x2 - 10x + 85 ) ) + -1 ( | 3x - 717 - x | ) be ( , ]. Then + is equal to :
- 12
- 8
- 10
- 9
Answer
(4) 9
Solution
For 3: 5 (7 - 2(x2 - 10x + 85) ) > 0
7 - 2(x2 - 10x + 85) > 1
x2 - 10x + 85 < 26 = 64 (x2 - 10x + 85 > 0 always)
x2 - 10x + 21 < 0 (x - 3)(x - 7) < 0 3 < x < 7 ...(i)
For -1: | 3x - 717 - x | 1, x 17
(3x - 7)2 (17 - x)2
8x2 - 8x - 240 0 (x - 6)(x + 5) 0 -5 x 6 ...(ii)
From (i) and (ii): domain = (3, 6] ⇒ = 3, = 6
+ = 9
Answer: (4)