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**hatsoff** Close, but not quite. You can't take the integral of $\displaystyle f(u)$ with respect to $\displaystyle x$. So, since we substituted $\displaystyle u$ for $\displaystyle sin(x)$, you also need to get rid of $\displaystyle cos(x)$ and $\displaystyle dx$ for something in terms of $\displaystyle u$.

We know:

$\displaystyle u=sin(x)$

So, take the derivative of that to get:

$\displaystyle du/dx=cos(x)$

$\displaystyle du=cos(x)dx$

Then finish your substitution, and you'll be ready to integrate.