Question

17. प्रमाणित गर्नुहोस् (Prove that): 3 cos3a C003a . + + ) = cosa + cos(120° + a) + cos(240° + a) 4 (Ans:(2-1)​

Answer 1

Answer:

we know cos3A=4 cos^3 A - 3 cosA

cos^3A = 1/4(cos3A +3 cosA)

=1/4(cos3A+3cosA) + 1/4[cos(360+3A) + 3 cos(120+A)] + 1/4[cos(360-3A) + 3 cos(120-A)]

=3/4 cos3A + 1/4 [ 3cosA + 3.2(cos120 cosA)]

= 3/4 cos3A + 1/4[3cosA-3cosA]

= 3/4 cos3A

Explanation:

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