f(x)=3x-1/x^3
f"(x)=?
f(x)=x*cosx
f"(3)=?

f(x)=3x-1/x^3f'=((3*x^3)-(2x^2)*(3x-1))/x^6=(3x^3-6x^3+2x^2)/x^6=-3x^3+2x^2/x^6f"=(-3x^3+2x^2)' *(x^6)- (-3x^3+2x^2)*(x^6)'f=x*cosxf'=cosx-x*sinxf"=-sinx-sinx-x*cosx=-2sinx- x*cosx