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JEE Mains · Maths · STD 12 - 1. relation and function

Let \({f_k}\left( x \right) = \frac{1}{k}\left( {{{\sin }^k}x + {{\cos }^k}x} \right)\;,x \in R\) and \(k \ge 1\), then \({f_4}\left( x \right) - {f_6}\left( x \right)\) is equal to

  1. A \(\frac{1}{4}\)
  2. B \(\frac{1}{{12}}\)
  3. C \(\frac{1}{6}\)
  4. D \(\frac{1}{3}\)
Verified Solution

Answer & Solution

Correct Answer

(B) \(\frac{1}{{12}}\)

Step-by-step Solution

Detailed explanation

\(f_{4}(x)-f_{6}(x)=\frac{1}{4}\left(\sin ^{4} x+\cos ^{4} x\right)-\frac{1}{6}\) \(\left(\sin ^{6} x+\cos ^{6} x\right)\) \(=\frac{1}{4}\left(1-2 \sin ^{2} x \cos ^{2} x\right)-\frac{1}{6}\left(1-3 \sin ^{2} x \cos ^{2} x\right)\)…
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