Ok I know you have to do trig substitution but its been awhile since I've done so : /
The problem is : The integral of 2Sqrt(1-x^2)
I think if $\displaystyle \sqrt{a^2 -x^2}$ occurs in an integrand, you have to try the substitution $\displaystyle x=a sin \theta$. In this case a=1.
EDIT: I will show you one more step:
Since $\displaystyle x=a sin \theta$ implies that $\displaystyle \theta = sin^{-1} x$
Therefore, $\displaystyle dx = cos \theta d \theta$. Can you continue from here?
The original posted question was wrong. See here: http://www.mathhelpforum.com/math-he...tml#post413788
This thread is being kept open in case other members want to follow up on the posted question.
You might find this website useful: - Wolfram|Alpha
Be sure to click on Show steps.