A)f'(x)=14x-56; f'(4)=14*4-56=0
b)f'(x)=(4*(x^2+4)-2x*4x) /(x^2+4)^2=(4x^2+16-8x^2)/(x^2+4)^2=
=16-4x^2)/(x^2+4)^2; f'(0)=16/(4^2)=16/16=1
c)((x^2+1)(x^3-2))'=(2x(x^3-2)+3x^2 *(x^2+1)=2x^4-4x+3x^4+3x^2=
5x^4+3x^2-4x;
f'(x)=5x^4+3x^2-4x; f'(1)=5+3-4=4
d)(3xsinx)'=3sinx+3x*cosx;
f'(x)=3sinx+3xcosx; f'(π/3)=3*sin(π/3) +3*(π/3)cos(π/3)=3√3/2 +π*(1/2)=
=(3√3+π)/2