Principle Of Mathematical Induction

Question
CBSEENMA11014315

Prove that:
2 cosA cosB = cos (A + B) + cos (A - B)




Solution

R.H.S. = cos(A + B) + cos(A - B)
          = [cosA cosB - sinA sinB] + [cosA cosB + sinA sinB]
          = 2 cosA cosB = L.H.S.
Hence,        2 cosA cosB = cos (A + B) + cos (A - B)

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