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1.If sin x + sin2x + sin3x= 1, then cos6x-4cos4x+8cos2x = (a) 2 (b) 1 (c) 3 (d) 4

1.If sin x + sin2x + sin3x= 1, then
cos6x-4cos4x+8cos2x =

(a) 2

(b) 1

(c) 3

(d) 4

Grade:11

1 Answers

SAGAR SINGH - IIT DELHI
879 Points
10 years ago

Dear student,

It's probably not in the spirit of the question but you can just solve that cubic numerically and get sin(x) = 0.5437. Then using cos^2(x) = 1- sin^2(x) you can easily evaluate it.

The answer will be 4.

Please feel free to ask your queries here. We are all IITians and here to help you in your IIT JEE preparation.

All the best.

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