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Explain solution RD Sharma class 12 chapter Determinants exercise multiple choise question 28 maths

Answers (1)

Answer:

Correct option (a)

Hint:

First solve the given determinant then find the maximum value of sin function, which is 1.

Given:

Given that,

        \Delta =\begin{vmatrix} 1 &1 &1 \\ 1 &1+sin\, \theta &1 \\ 1+cos\, \theta &1 &1 \end{vmatrix}

We have to find the maximum value of \Delta.

Solution:

Here\: \: \Delta =\begin{vmatrix} 1 &1 &1 \\ 1 &1+sin\, \theta &1 \\ 1+cos\, \theta &1 &1 \end{vmatrix}

Applying R1 → R1 - R2

        \Rightarrow \Delta =\begin{vmatrix} 1 &1 &1 \\ 1 &1+sin\, \theta &1 \\ 1+cos\, \theta &1 &1 \end{vmatrix}

Expanding along R1

        \begin{aligned} &\Rightarrow \quad \Delta=\sin \theta[1-1-\cos \theta] \\ &\Rightarrow \quad \Delta=-\sin \theta \cos \theta \\ &\Rightarrow \quad \Delta=\frac{-2 \sin \theta \cos \theta}{2} \\ &\Rightarrow \quad \Delta=\frac{-\sin 2 \theta}{2} \end{aligned}            [\because \sin \sin 2 \theta=2 \sin \sin \theta \cos \cos \theta]

We know that the maximum value of sin function is 1.

Hence, maximum value of

        \Delta =\frac{1}{2}

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Gurleen Kaur

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