Giúp mình câu 21,22 với

$21)f(x)e^x=(sin3x)'=3cos3x\\ u=e^x=>du=e^xdx\\ dv=f'(x)dx=>v=f(x)\\ \int f'(x).e^x \, dx=f(x)e^x-\int f(x).e^x \, dx=3cos3x-sin3x+C\\ =>A\\ 22)\int f'(x)f(x)\, dx=\int (x^4+x^2) \, dx\\ <=>\int f(x)\, d( f(x))=\dfrac{1}{5}x^5+\dfrac{1}{3}x^3+C\\ <=>\dfrac{1}{2}f(x)^2=\dfrac{1}{5}x^5+\dfrac{1}{3}x^3+C\\ f(0)=2=>C=2\\ =>f(x)^2=\dfrac{2}{5}x^5+\dfrac{2}{3}x^3+4\\ =>f(2)^2=\dfrac{332}{15}\\ =>B$