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If Sin a+ sin 2 a=1 then,find the value of cos 12 a +3cos 10 a+3cos 8 a+cos 6 a-1


If Sin a+ sin2a=1 then,find the value of   cos12 a +3cos 10a+3cos 8a+cos 6a-1

Grade:11

1 Answers

Pramod J AskiitiansExpert-IIT-B
36 Points
9 years ago

Dear student,

cos12 a +3cos 10a+3cos 8a+cos 6a-1

can be written as [cos^2 a + cos^4 a]^3 - 1

from given equation sin^2 a  = 1 - sin a => cos^2 a = sin a

=> [ sina a + sin^2 a ]^3 - 1 

=> 1^3 - 1

=> 0

hope it explains !!

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