integral of 1/(9 + 4x^2)

The book says u should be 2/3x. Can someone enlighten me on why this is? I amdumbfounded :(

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- February 22nd 2009, 05:49 AMTYTYconfused with u-subs problem
integral of 1/(9 + 4x^2)

The book says u should be 2/3x. Can someone enlighten me on why this is? I am**dumb**founded :( - February 22nd 2009, 05:54 AMmr fantastic
- February 22nd 2009, 06:02 AMTYTY
please be patient with me here as I still don't understand this. (2x/3)^2 x 9 would have to equal 4x^2 again here right? but wouldn't it be (18x/3)^2 = 6x^2?

edit: I guess because of the square, you simplify using square root or something. The calculator agrees with your result but somehow it still goes over my head :( - February 22nd 2009, 06:15 AMmr fantastic
- February 22nd 2009, 06:20 AMTYTY