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if A+B+C=pi prove that a)cos(B-C)+cosA=2sinBsinC

if A+B+C=pi prove that
a)cos(B-C)+cosA=2sinBsinC
 

Grade:12th pass

1 Answers

ng29
1698 Points
8 years ago
its quite easy , in this type of questions generally substitute one angle in terms of other
put A= pi -(B+C)   
now cos A  becomes cos(pi -(B+C)) =  – cos(B+C)
now  u can easily get answer
 
 
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