Anonymous

# prove that sin(a+b+c)= sina+cosb+cosc+sinb+cosa+cosc+sinc+cosb+cosa-sina-sinb-sinc?

thanx

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- 10 years agoFavourite answer
Use the formula

sin(a + b) = sina cosb + sinb cos a

Then sin(a + b + c)

= sin((a + b) + c)

= sin(a + b) cosc + cos(a + b) sin c

Then use the formula

cos(a + b) = cosa cosb - sina sinb to get

sin(a + b) cosc + cos(a + b) sin c

= (sina cosb + sinb cosa) cosc + (cosa cosb - sina sinb) sinc

= sina cosb cosc + sinb cosa cosc + sinc cosa cosb - sina sinb sinc

- Stephan BLv 510 years ago
you seem to be missing a bit, but what, for instance does sin (x+y) equal, in terms of x and y?

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