Prove the following identity. ?

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1 Answer
Somebody N.
Feb 20, 2018

See below.

Explanation:

Identities.

#color(red)bb(cos(A-B)=cosAcosB+sinAsinB)#

#color(red)bb(cos(A+B)=cosAcosB-sinAsinB)#

#RHS#

#cos(x-y)=cosxcosy+sinxsiny#

#cos(x+y)=cosxcosy-sinxsiny#

#cos(x-y)-cos(x+y)=#

#-> (cosxcosy+sinxsiny)-(cosxcosy-sinxsiny)=#

#->cosxcosy+sinxsiny-cosxcosy+sinxsiny=#

#->2sinxsiny#

#LHS!=RHS#

Not possible to solve.

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