f'(x)=1/6 *6x^5 -3*2x = x^5-6x
f'(2)=2^5-6*2=32-12=20
f'(x)=2x-1/x^2
f'(-1)=2*(-1) -1/(-1)^2 = -2-1=-3
f'(x)=3x^2 *(3x^2+1) + (x^3-4)*6x
f'(2)=3*2^2 *(3*2^2+1)+(2^3-4)*6*2= 12*13+48=156+48=204
f'(x)=5*cosx -5x*sinx
f'(p/2) = 5 cos p/2 - 5p/2 * sin p/2 = 5*0 - 5p/2*1= -5p/2