Suy được: [tex]f^2(x).f'(x)=\frac{1}{9}[/tex]
Có: [tex]\int f^2(x).f'(x)dx=f^3(x)-2\int f^2(x).f'(x)dx\\\Rightarrow f^3(x)=3\int f^2(x).f'(x)dx\\\Rightarrow f^3(x)=3\int \frac{1}{9}dx\\\Rightarrow f^3(x)=\frac{1}{3}x+C\\f(0)=1\Rightarrow C=1\\\Rightarrow f^3(x)=\frac{1}{3}x+1\\\Rightarrow \int_{0}^{1}f^3(x)dx=\int_{0}^{1}(\frac{1}{3}x+1)dx=\frac{7}{6}[/tex]