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December 22, 2014

December 22, 2014

Posted by **Alice** on Saturday, February 21, 2009 at 4:23pm.

work on one side only...so i worked on the right

=(sinx-siny)(sinx+siny) does that equal

sin(x-y)sin(x+y)??? help!

- Trig -
**drwls**, Saturday, February 21, 2009 at 5:50pmUse the formulas for sin (A-B) and sin (A+B)

The left side is

(sinx cos y - siny cosx)(sinx cosy + siny cosx)

= sin^2x cos^2y - sin^2y cos^2 x

=(1 - cos^2x)(cos^2y)-sin^2y cos^2x

= cos^2y -cos^2y cos^2x - sin^2y cos^2x

= cos^2y -cos^2x

= 1-sin^2y -1 + sin^2x

= sin^2x - sin^2y

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