Let the set of all values of p R, for which both the roots of the equation x2 - (p + 2)x + (2p + 9) = 0 are negative real numbers, be the interval ( , ]. Then - 2 is equal to
- 5
- 0
- 20
- 9
Answer
(1) 5
Solution
Both roots negative real numbers:
(i) D ≥ 0: (p + 2)2 - 4(2p + 9) 0 p2 - 4p - 32 0
(p - 8)(p + 4) 0 p -4 or p 8
(ii) Sum of roots < 0: p + 2 < 0 p < -2
(iii) Product of roots > 0: 2p + 9 > 0 p > - 92
p (- 92, -4 ] = - 92, = -4
- 2 = -4 + 9 = 5
Answer: (1)