Prove that cos80+cos40-cos20=0

steps to prove cos80+cos40-cos20=0

Take L.H.S cos80+cos40-cos20

=cos80+cos40-cos20

=cos(60+20)+cos(60-20)-cos20

=2cos60.cos20-cos20

=2x1/2cos20-cos20

=cos20-cos20

=0

=R.H.S

Hence cos80+cos40-cos20=0 is Proved

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