# Math Help - Integeral: Trig Substitution help

1. ## Integeral: Trig Substitution help

I have this equation

So I refer to a triangle and use these values for substitution.

$\sqrt[]{25-x^{2}}$ = 5 cos(x)

x = 5 sin(x)

dx = 5 sin(x) = 5 cos(x)

I ended up having something like this.

I canceled the 5 sin(x)s leaving me with

integral(5 cos x) = - 5 sin x + c

I looked at the triangles and got back.

x/5 + c

Then I looked back at the book for answers and I was way way way off.

What did I do that was totally wrong?

2. hey man i dont think u set up your triangle properly.. it should be (25-x^2)^1/2 divided by 5

3. a = sqrt(25-x^2)
b = x
c = 5

^ I thought that is how you normally set it up for a sqrt(c^2 - x^2) situation where c is a constant.

4. No that's wrong. You solved for it. Cos=x/5 so adjacent is x and 5 is the hypotnuse using pythagorems theorm you can solve for the other side