# cos(sqrt x)

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• August 3rd 2009, 07:08 AM
fadeer
cos(sqrt x)
HELLO,

I d be grateful to anyone who solves the following, as I have been trying for ages but it is not working.

Q/ solve by finding appropriate substitution and then integrate by parts:
integral of cos(sqrt x).

Thanks.
• August 3rd 2009, 07:22 AM
CaptainBlack
Quote:

Originally Posted by fadeer
HELLO,

I d be grateful to anyone who solves the following, as I have been trying for ages but it is not working.

Q/ solve by finding appropriate substitution and then integrate by parts:
integral of cos(sqrt x).

Thanks.

What is wrong with $u=\sqrt{x}$, then integrate by parts

CB
• August 3rd 2009, 07:29 AM
fadeer
I am sorry but could you make it a little clearer.
Thanks.
• August 3rd 2009, 07:37 AM
CaptainBlack
Quote:

Originally Posted by fadeer
I am sorry but could you make it a little clearer.
Thanks.

If $u=\sqrt{x}$ we have:

$
\int \cos(\sqrt{x})\; dx=\int \cos(u) \frac{dx}{du}\;du=2 \int u\cos(u)\;du
$

and now you use integration by parts.

(If you need more help WolframAlpha will give you a step by step explanation of the complete process)

CB
• August 3rd 2009, 07:45 AM
fadeer
Thanks a lot bro,

No need bcz I know to complete it.
I was stuck with the substitution part.

I appreciate ur help.