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Question 9
If
sinA+sin2A=1, then the value of (cos2A+cos4A) is

(A) 1
(B) 12
(C) 2
(D) 3


Solution

The answer is (A).

Given, sinA+sin2A=1

sinA=1sin2A=cos2A    [sinθ+cos2θ=1]

On squaring both sides we get,

sin2A=cos4A

1cos2A=cos4A

cos2A+cos4A=1(Ans.).

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