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Previous Year Question (PYQs)
1
Let m and M be respectively the minimum and maximum values of
\[
\left|
\begin{array}{ccc}
\cos^{2}x & 1+\sin^{2}x & \sin 2x\\
1+\cos^{2}x & \sin^{2}x & \sin 2x\\
\cos^{2}x & \sin^{2}x & 1+\sin 2x
\end{array}
\right|.
\]
Then the ordered pair (m, M) is equal to :
Solution
Let $m$ and $M$ be respectively the minimum and maximum values of
\[
\left|\begin{matrix}
\cos^2 x & 1+\sin^2 x & \sin 2x\\
1+\cos^2 x & \sin^2 x & \sin 2x\\
\cos^2 x & \sin^2 x & 1+\sin 2x
\end{matrix}\right|.
\]
Then the ordered pair $(m, M)$ is equal to :
Solution:
Apply $R_2 \to R_2 - R_1$ and $R_3 \to R_3 - R_1$
\[
\Delta =
\left|\begin{matrix}
\cos^2 x & 1+\sin^2 x & \sin 2x\\
1 & -1 & 0\\
0 & -1 & 1
\end{matrix}\right|
\]
Expanding along the first row,
\[
\Delta = \cos^2 x(-1) - (1+\sin^2 x)(1) - \sin 2x(1)
\]
\[
\Delta = -(\cos^2 x + \sin^2 x + 1 + \sin 2x)
\]
\[
\Delta = -2 - \sin 2x
\]
Since $\sin 2x \in [-1,1]$,
\[
\Delta \in [-3, -1]
\]
Hence, $m = -3$, $M = -1$
Therefore, the ordered pair is $\boxed{(-3, -1)}$.
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