Question

If f(x)= 2x^3 -4x , find f'(3)

Answer 1

Find the derivative
Then put x = 3 and evaluate the derivative.

Answer 2

Yeah but can you please find the derivative ?

Answer 3

Derivative of x^n is nx^(n-1)
f(x) = 2x^3 - 4x
f'(x) = d/dx(2x^3 - 4x) = d/dx(2x^3) - d/dx(4x) = 2 * d/dx(x^3) - 4 * d/dx(x)
= 2 * (3x^2) - 4 * (1)
f'(x) = 6x^2 - 4
f'(3) = 6(3)^2 - 4 = 54 - 4 = 50