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TS EAMCET · Maths · Functions

The function \(f: R \rightarrow R\) is defined by \(f(x)=\cos ^2 x+\sin ^4 x\) for \(x \in R\), then \(f(R)\) is equal to

  1. A \(\left(\frac{3}{4}, 1\right]\)
  2. B \(\left[\frac{3}{4}, 1\right)\)
  3. C \(\left[\frac{3}{4}, 1\right]\)
  4. D \(\left(\frac{3}{4}, 1\right)\)
Verified Solution

Answer & Solution

Correct Answer

(C) \(\left[\frac{3}{4}, 1\right]\)

Step-by-step Solution

Detailed explanation

We have, \[ \begin{aligned} & f(x)=\cos ^2 x+\sin ^4 x=1-\sin ^2 x+\sin ^4 x \\ & =1-\sin ^2 x\left(1-\sin ^2 x\right)=1-\sin ^2 x \cos ^2 x \\ & =1-\frac{1}{4} \sin ^2 2 x \end{aligned} \]…