Can someone please check my answer: Trig Substitution problem

[jimen113]

I tried to use the latex reference but it was way too complicated for me.
Can you see the attachment.
Thank you!

 

[HallsofIvy]

If you are letting x= cos(\theta) then dx= cos(\theta)d\theta. It looks to me like you forgot that cos(\theta).

 

[jimen113]

Thank you HallsofIvy for your help.
Yes it did forget! but wouldn't by dx= sin \vartheta
please see the updted the attachment.

 

[Mark44]

If x = cos(\theta), then dx = -sin(\theta)d\theta

 

[HallsofIvy]

Yes, of course Mark44 is right. I don't know what came over me!

 

[jimen113]

Thanks Mark44! that negative sign is sure important...