>>84124f(x) = 2x^2 + 8x^2 + 2x - 11
f(x) = 10x^2 + 2x - 11
Integrate so increase power by 1 then divide by the new power
f'(x) = 10/3x^3 + x^2 - 11x
4x = 10/3x^3 + x^2 - 11x
10/3x^3 + x^2 - 15x = 0
Differentiate it to get
3* 10/3x^2 + 2*x - 15 = 0
10x^2 + 2x - 15 = 0
(x + 5)(x - 3) = 0
Therefore x = -5 and x = 3
