1.

What is the value of x if, \(\begin{vmatrix}x & 3 & 6 \\3 & 6 & x \\6 & x & 3 \end {vmatrix}\) = \(\begin{vmatrix}2 & x & 7 \\x & 7 & 2 \\7 & 2 & x \end {vmatrix}\) = \(\begin{vmatrix}4 & 5 & x \\5 & x & 4 \\x & 4 & 6 \end {vmatrix}\)?(a) 9(b) -9(c) 0(d) Can’t be predictedThe question was asked in an interview.My doubt is from Application of Determinants topic in section Determinants of Mathematics – Class 12

Answer»

Right answer is (b) -9

Easy EXPLANATION: GIVEN that,

\(\begin{vmatrix}x & 3 & 6 \\3 & 6 & x \\6 & x & 3 \end {vmatrix}\) = \(\begin{vmatrix}2 & x & 7 \\x & 7 & 2\\7 & 2 & x \end {vmatrix}\) = \(\begin{vmatrix}4 & 5 & x \\ 5 & x & 4 \\x & 4 & 6 \end {vmatrix}\)

So, by circular DETERMINANT property,

Sum of the elements of a row = 0

So, x + 3 + 6 = 2 + x + 7 = 4 + 5 + x = 0

=> x = -9



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