Mark (√) against the correct answer in the following:
If is increasing for every real number x, then
Given f(x) = kx3 -9x2+ 9x+3
⇒ f’(x) = 3kx2-18x+9
⇒ f’(x) = 3(kx2 – 6x + 3)>0
⇒ kx2 – 6x + 3 >0
For quadratic equation to be greater than 0. a>0 and D<0.
⇒ k>0 and (-6)2- 4(k)(3)<0
⇒ 36 – 12k<0
⇒ 12k>36
⇒ k>3
∴ k>3.