Question

prove that cos42+cos78+cos162=0​

Answer 1

Answer:

cos42+cos78+cos162=0

cos(60-18)+cos(60+18)+cos(180-18)=0

now apply formula,

cos60.cos18+sin60.sin18+cos60.cos18-sin60.sin18-cos18=0

2×1/2.cos18-cos18=0

cos18=cos18

L.H.S =R.H.S PROVED.

Step-by-step explanation:

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