(x-3)(x^2+3x+9)=x^3-27
y'=3x^2
y'(3)=27
y=(x-3)(x^2+3x+9)
y=(x^3+3x^2+9x-3x^2-9x-27)
y=x^3-27
y'=(x^3-27)'=3x^2
y(3)=0
