Question

If , then x is equal to (A) 6 (B) ±6 (C) −6 (D) 0

Answer 1

Take matrix,

[ x 2 18 x ]

Determinant of the given matrix is,

| x 2 18 x | = x 2 −2×18 = x 2 −36 (1)

Now, determinant of the right hand side matrix is,

| 6 2 18 6 | =36−36 =0 (2)

As per the given question, equation (1) is equal to equation (2).

So,

x 2 −36=0 x 2 =36 x=±6

The value of x is ±6.

Thus, the correct answer is ( B ).