TULICOL Ullege bas If sin x + sin2 ...
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TULICOL Ullege bas If sin x + sin2 x = 1, then cos8 x + 2 cos6 x + cos4 x = .... (A) 0 (B) - 1 (C) 2 (D) 1

JEE/Engineering Exams
Maths
Solution
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( sin x+sin ^{2} x=1 ) ( sin x=1-sin ^{2} x ) ( sin x=cos ^{2} x ) ( sin ^{2} x=cos ^{4} x ) SO, ( cos ^{wedge} 8 x+2 cos ^{wedge} 6 x+cos ^{4} x ) ( =cos ^{4} xleft(cos ^{4} x+2 cos ^{2} x+1right) ) ( =sin ^{2} xleft(sin ^{2} x+2 sin x+1right) ) ( =sin ^{4} x+2 sin ^{3} x+sin ^{2} x ) ( =sin ^{4} x+sin ^{3} x+sin ^{3} x+sin ^{2} x ) ( =sin ^{2} xleft(sin ^{2} x+sin xright)+sin xleft(sin ^{2} x+sin xright) ) ( =sin ^{2} x times(1)+sin x(1) ) ( =sin ^{2} x+sin x ) ( =1 ) İs your final answer
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