$\displaystyle \int5x\sqrt[3]{1-x^2}dx$

I am required to use U subsitiution.

u= $\displaystyle 1-x^2$

du= $\displaystyle -2x $ $\displaystyle dx$

So the problem became....

$\displaystyle \frac{-2}{5} \int u^{1/3} du$

and my final answer was...

$\displaystyle \frac{-3}{10} u^{4/3} + C$

This seems correct to me, however the answer my book gives is...

$\displaystyle \frac{-15}{8} u^{4/3} + C$

Of course I will replace the u in the final answer, but I cannot figure out how the book did this problem. Can someone please tell me what I did wrong.

Thanks so much!