Question

If sin A + sin2A = 1,then cos2A +cos 4A is a) -1 b) c) d) none of these​

Answer 1

Answer:

1

Step-by-step explanation:

sinA+sin2A=1

⇒sinA=1−sin2A

⇒sinA=cos2A

⇒cos2A+cos4A=cos2A[1+cos2A]

=sinA[1+sinA]

=sinA+sin2A

=1

Hence, the answer is 1.

Answer 2

ans;          cos2A+cos4A =COS2A+(1-2SIN^2A)                                                                                                =(2COS^2A-1) +1-2(1-SIN^2A) =0