# Thread: Small integral problem (one step)

1. ## Small integral problem (one step)

I'm not great when it comes to integrals.

I have

Sin^2(2x)

I know Sin(x) goes to -Cos(x), and Sin(2x) would go to -Cos(2x)(2), right?

I just don't know how to approach Sin^2(2x)

thanks

2. $\displaystyle \sin^22x=\frac{1-\cos 4x}{2}$

3. I have a follow up question.

Doing a seperate part of the same question, I have xsin(2x)

Would this be [(x^2)(-cos(2x)(2)]/2 ?

4. Originally Posted by JTG2003
I have a follow up question.

Doing a seperate part of the same question, I have xsin(2x)

Would this be [(x^2)(-cos(2x)(2)]/2 ?
no ... $\displaystyle \int x \sin(2x) \, dx$ has to be done by parts.

5. Originally Posted by skeeter
no ... $\displaystyle \int x \sin(2x) \, dx$ has to be done by parts.

Done by parts? Sorry, I don't know what you mean by that ...

6. Originally Posted by JTG2003
Done by parts? Sorry, I don't know what you mean by that ...
Integration by parts.

If you don't know this technique then I don't know why you'd be asked to solve this integral (unless you were previously asked to find the derivative of $\displaystyle x \cos (2x)$).

7. Sorry, I'm taking calc + calc II as summer classes.. it's all going very fast. I'm having a hard time keeping up.

8. Originally Posted by JTG2003
Sorry, I'm taking calc + calc II as summer classes.. it's all going very fast. I'm having a hard time keeping up.
recommend you visit this site ... it has much help to offer you in your current academic predicament

Pauls Online Notes : Calculus II - Integration by Parts