CGGO Q23
23The entire graph of the function f(x) = x2 + kx - x + 9 is strictly above the x-axis if and only if
- Option : D
- Explanation : y = x2 + (k- 1) x + 9 = (x + (k -1)/2)2 - ((k- 1)/2) + 9 For the entire graph to lie above the x-axis. y should be greater than 0, for all x. So, 9 - ((k- 1)/2) 2 > 0 i.e., (k - 7) (k + 5) < 0 or - 5 < k < 7
