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- July 3rd 2009, 02:24 AM #1

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## [SOLVED] (7cosx+5sinx)²=Acos2x+Bsin2x+C

Hello there

I need help with the following trig question...

(7cosx+5sinx)²=Acos2x+Bsin2x+C

I've come about this far...

(7cosx+5sinx)²=24cos²x+35sin2x+25

I need to do something about the 24cos²x but im unsure how to proceed... I was thinking i could use cos²(x/2)=(1+cosx)/2

but im not sure...

Thanks in advance

Janne the Swede

- July 3rd 2009, 03:19 AM #2

- July 3rd 2009, 03:44 AM #3

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- July 3rd 2009, 04:06 AM #4