# Math Help - integrals by substitution

1. ## integrals by substitution

$\int (1/ \sqrt{x})\ sin\sqrt{x}\ dx\
u=\sqrt{x}\$

the answer is $-2cos(\sqrt{x})+C$ but cant seem to get there

2. Originally Posted by vinson24
$\int (1/ \sqrt{x})\ sin\sqrt{x}\ dx\
u=\sqrt{x}\$

the answer is $-2cos(\sqrt{x})+C$ but cant seem to get there
Since they let $u=\sqrt{x}$, this implies that $\,du=\frac{\,dx}{2\sqrt{x}}$

Now, we see that $\int\frac{1}{\sqrt{x}}\sin\sqrt{x}\,dx\implies 2\int\frac{1}{2\sqrt{x}}\sin\sqrt{x}\,dx\implies 2\int\sin u\,du$

Can you take it from here?

--Chris

3. let u = sqrt x
du = dx / 2sqrt x

substitute to the equation you will get, the following

2 integrate sin u du

I think you should be able to take it from here.

4. thanks see it now

5. You need to put 2 outside of the integration to take care of the 1/2 that is inside the equation. If you do not put the 2 outside. The original equation would have been changed. The 2 is to prevent that from happening Hope it helps.