If sinx+sin2x=1, then the value of cos12x+3cos10x+3cos8x+cos6x−2 is equal to
A
0
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B
1
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C
−1
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D
2
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Solution
The correct option is C−1 sinx+sin2x=1⇒sinx=1−sin2x⇒sinx=cos2x ...(1) cos12x+3cos10x+3cos8x+cos6x−2 Substituting values from (1), we get sin6x+3sin5x+3sin4x+sin3x−2=(sin2x+sinx)3−2=1−2=−1