Homework Help: trig sub question

Posted by Tom on Friday, February 22, 2013 at 6:30pm.

Hello, I have a question concerning trigonometric substitution.

let's say we have

integral of dx/sqrt(9x^2 + 4),

so after doing a few steps we have:

2/3 integral of sec0/sqrt((2tan0)^2 + 4*) d0 (the * is for later on)

the next step turns into:

2/3 integral of sec0/(sqrt(4tan^2 0 + 1))

I know that the sqrt(4 tan^2 0 + 1) is because of the power of 2 from the first step, but where does the other + 4 disappear (the one I put a * next to).

trig sub question - Steve, Saturday, February 23, 2013 at 5:07am
You need 3x = 2tanθ, so
9x^2 = 4tan^2 θ
9x^2+4 = 4tan^2 θ + 4 = 4sec^2 θ
trig sub question - Tom, Saturday, February 23, 2013 at 8:57am
thank you Steve

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