If the set of all a R - \1\, for which the roots of the equation (1 - a)x2 + 2(a - 3)x + 9 = 0 are positive is (- , - ] [ , ), then 2 + + is equal to .
Answer
7
Solution
Both roots positive needs (i) real roots, (ii) sum > 0, (iii) product > 0.
(i) D 0: 4(a - 3)2 - 36(1 - a) 0
a2 - 6a + 9 - 9 + 9a 0 a(a + 3) 0
a -3 or a 0
(iii) Product = 91 - a > 0 a < 1
(ii) Sum = -2(a - 3)1 - a = 2(3 - a)1 - a > 0, true for every a < 1
Combining: a (- , -3] [0, 1)
= 3, = 0, = 1
2 + + = 6 + 0 + 1 = 7
Answer: 7