Q : 8        If   \begin{vmatrix}x &2 \\18 &x \end{vmatrix}=\begin{vmatrix} 6 &2 \\ 18 &6 \end{vmatrix} ,  then x is equal to

                (A) 6        (B) \pm 6       (C) -6     (D) 0

Answers (1)

Solving the L.H.S. determinant ;

\dpi{100} \begin{vmatrix}x &2 \\18 &x \end{vmatrix}= x^2 - 36

and solving R.H.S determinant;

\begin{vmatrix} 6 &2 \\ 18 &6 \end{vmatrix} = 36-36 = 0

So equating both sides;

x^2 - 36 =0        or     x^2 = 36        or     x = \pm 6

Hence answer is (B).

 

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