-x^2+4x=0 -x*(x-4)=0 x_(1)=0; x_(2)=4 [m]S= ∫ ^{4}_{0}(-x^2+4x)dx=(-\frac{x^3}{3}+4\cdot \frac{x^2}{2})| ^{4}_{0}=-\frac{4^3}{3}+2\cdot 4^2=\frac{32}{3}[/m]