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tmlsrock1

Member

Registered: 2007-12-16

Posts: 0

trig identity

how do you prove sin(a+b+c)=sinacosbcosc+cosasinbcosc+cosacosbsinc-sinasinbsinc?

mathsyperson

Moderator

Registered: 2005-06-22

Posts: 4,900

Re: trig identity

First substitute a+b = p, and find sin(p+c).
Your answer will be in terms of sinp, cosp, sinc, and cosc.

Replace the sin(p)'s with sin(a+b)'s and the cos(p)'s with cos(a+b)'s, and then use the addition identities to get an answer in terms of sines and cosines of a, b and c.

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tmlsrock1

Member

Registered: 2007-12-16

Posts: 0

Re: trig identity

thanks