f(x) = 40 x+ 5t
f(x) = x2-5x
f(x) = (1/2)x4-7x2+10k
f(x) = 1/(x2+10)
f(x) = 3x3-6x2+7
f'(x)=-x3
f'(x) = 2x3-14x
f'(x) = 9x2-12x
f'(x) = 40
f'(x) = 2x-5
