Find the derivative of f(x)=7x3−4x2f(x) = 7x^3 - 4x^2f(x)=7x3−4x2.
21x2−8x21x^2 - 8x21x2−8x
7x2−4x7x^2 - 4x7x2−4x
21x3−8x221x^3 - 8x^221x3−8x2
21x2−421x^2 - 421x2−4