Question

cos2A+cos2B+Cos2C+cos2(A+B+C)=4cos(B+C)cos(C+A)cos(A+B) prove that

Answer 1

= 2cos(A + B)cos (A-B) + 2cos(A +B + 2C)cos(A+B)
= 2cos(A +B){ cos (A-B) + cos (A+ B+ 2c)}
= 2cos (A+ B) {2cos(B +C)cos (A + C)
= 4 cos(A +B)cos(B+C)cos(A+C)
hence,proved

Answer 2

Step-by-step explanation:

Hope it helps.

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