Trigono

A+B+C=Î 2
p.t. +cos2A+cos2B+cos2C=2(1+sinAsinBsinC)

1 Answers

591
Akshay Ginodia ·

Proceed from the RHS,

2+ (2sinAsinB)sinC
= 2+ {cos(A-B)-cos(A+B)}sinC
=2+ {cos(A-B) - cos (Ï€/2 - C)} sinC
=2+ cos(A-B)sinC - sin2C
Now in cos(A-B)sinC again apply the formula for sinAcosB and proceed..

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