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## Homework Statement

Integrate (9x

^{2}-16)

^{1/2}/x

^{4}

## Homework Equations

## The Attempt at a Solution

I set 3x=4secy, 3dx=4secytany and (9x

^{2}-16)

^{1/2}=2tany.

I then plugged that all into my integral and ended up with2tany*4secytany/(4/3secy)

^{4}dy...

(81/32) tan

^{2}y/sec

^{3}y dy....

I solved for this by switching tan and sec to cos and sin, so (81/32) cos

^{3}y*sin

^{2}y/cos

^{2}y.... and integrated that to get (81/32)sin

^{3}/3+c.... when it's all worked out I had 32/x

^{3}

I can't figure out where I went wrong but I'm certain that I haven't got the right answer. Thanks!