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MHT CET · Maths · Trigonometric Equations

If \(\sin x+\sin ^{2} x=1\), then \(\cos ^{8} x+2 \cos ^{6} x+\cos ^{4} x\) is

  1. A 3
  2. B 2
  3. C 1
  4. D 4
Verified Solution

Answer & Solution

Correct Answer

(C) 1

Step-by-step Solution

Detailed explanation

Given \(\sin x+\sin ^{2} x=1 \Rightarrow \sin x=1-\sin ^{2} x\)
\(\begin{aligned} \therefore \sin x=\cos ^{2} x \Rightarrow \sin ^{2} x &=\cos ^{4} x \\ \cos ^{8} x+2 \cos ^{6} x+\cos ^{4} x &=\left(\cos ^{4} x+\cos ^{2} x\right)^{2} \\ &=\left(\sin ^{2} x+\cos ^{2} x\right)^{2}=1 \end{aligned}\)
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