My textbook says I should solve the following integral by first making a substitution, and then using integration by parts:
$$\int cos\sqrt x \ dx$$
The problem is, after staring at it for a while I'm still not sure what substitution I should make, and hence I'm stuck at the first step. I thought about doing something with the $\sqrt x$, but that doesn't seem to lead anywhere as far as I can tell. Same with the $cos$. Any hints?