503

$D\left(x^2+1\right)\left(x^2-1\right)$

$f\left(x\right)=x^2+1{,}\ f'\left(x\right)=2x\ ja\ g\left(x\right)=x^2-1{,}\ g'\left(x\right)=2x$

$D\left(f\left(x\right)\left(g\left(x\right)\right)\right)=f\left(x\right)g'\left(x\right)+f'\left(x\right)g\left(x\right)=\left(x^2+1\right)\cdot2x+2x\left(x^2-1\right)$
$=2x^3+2x+2x^3-2x=4x^3$

$\left(x^2+1\right)\left(x^2-1\right)=x^4-x^2+x^2-1=x^4-1=4x^3$