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how to prove a(cosB+cosC)=2(b+c)sin^2A/2

how to prove a(cosB+cosC)=2(b+c)sin^2A/2

Grade:11

1 Answers

SAGAR SINGH - IIT DELHI
878 Points
13 years ago

Dear student,

Use cosine law

cosB=a2+c2-b2/2ac

cosC=a2+b2-c2/2ab

Now prove LHS=RHS

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