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WBJEE · Maths · Determinants

If \(f:[0, \pi / 2) \rightarrow R\) is defined as
\(f(\theta)=\left|\begin{array}{ccc}1 & \tan \theta & 1 \\ -\tan \theta & 1 & \tan \theta \\ -1 & -\tan \theta & 1\end{array}\right|\) Then, the range of \(f\) is

  1. A \((2, \infty)\)
  2. B \((-\infty,-2]\)
  3. C \([2, \infty)\)
  4. D \((-\infty, 2]\)
Verified Solution

Answer & Solution

Correct Answer

(A) \((2, \infty)\)

Step-by-step Solution

Detailed explanation

We have, \(f(\theta)=\left|\begin{array}{ccc}1 & \tan \theta & 1 \\ -\tan \theta & 1 & \tan \theta \\ -1 & -\tan \theta & 1\end{array}\right|\) \(=1\left(1+\tan ^{2} \theta\right)-\tan \theta\) \((-\tan \theta+\tan \theta)+1\left(\tan ^{2} \theta+1\right)\)…