Posted by **Spencer** on Tuesday, January 20, 2009 at 7:34pm.

(cotxsec2x - cotx)/ (sinxtanx + cosx) = sinx

prove.

i keep getting (if i start from the left side) = cosx instead of sinx please help!

- trig -
**Reiny**, Tuesday, January 20, 2009 at 9:25pm
first of all you should have typed it correctly as

(cotxsec^2 x - cotx)/ (sinxtanx + cosx) = sinx

I read that first part as sec(2x), and wasted about 10 minutes trying to prove that.

so...

LS = [cotx(1/cos^2x - 1)]/[sin^2x/cosx + cosx]

= [cotx(1 - cos^2x)/cos^2x]/[(sin^x + cos^2x)cosx]

= [cotx(sin^2x/cos^2x)]/[1/cosx]

= [sinx/cosx]/[1/cosx]

= sinx

= RS

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