If the domain of the function f(x) = (10x2 - 17x + 7) (18x2 - 11x + 1 ) is (- , a) (b, c) (d, ) - \e\, then 90(a + b + c + d + e) equals:
- 170
- 316
- 177
- 307
Answer
(2) 316
Solution
Conditions: argument > 0, base > 0, base 1.
(i) 18x2 - 11x + 1 > 0 (9x - 1)(2x - 1) > 0 x < 19 or x > 12
(ii) 10x2 - 17x + 7 > 0 (10x - 7)(x - 1) > 0 x < 710 or x > 1
(iii) 10x2 - 17x + 7 1 10x2 - 17x + 6 0 (2x - 1)(5x - 6) 0 x 12, 65
Combining: domain = (- , 19 ) ( 12, 710 ) (1, ) - \ 65 \
a = 19, b = 12, c = 710, d = 1, e = 65
90(a + b + c + d + e) = 10 + 45 + 63 + 90 + 108 = 316
Answer: (2)