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Question

What is the determinant of the matrix?

| x      y      y+z |

 | z      x      z+x |

 | y      z      x+y |    

This question was previously asked in
NDA I 2018 GAT Previous Year Paper (22-Apr-2018)
The correct answer is

(x - z) 2 (x + y + z)

Quest

Find the determinant of the matrix:

| x      y      y+z | | z      x      z+x | | y      z      x+y |    

Solution (steps)

  1. Write the matrix and apply the column operation C3 ← C3 - C1 - C2. This operation does not change the determinant.
  2. Compute the new third column:C3' = (y+z) - x - y = z - x      (z+x) - z - x = 0      (x+y) - y - z = x - z So C3' = [z-x, 0, x-z]^T = (z-x)[1, 0, -1]^T        
  3. Factor out (z-x) from the third column. The determinant becomes(z - x) * det(  [ x  y  1 ]  [ z  x  0 ]  [ y  z -1 ] )        
  4. Evaluate the remaining 3×3 determinant. Expanding or computing directly yields (z - x)(x + y + z)(z - x), i.e. it contributes another factor of (z-x).
  5. Therefore the full determinant equals

\((x - z)^2 (x + y + z)\)

Final boxed answer: (x - z)2(x + y + z)

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Similar Questions

  1. If Δ(a, b, c, α) = 0 for every α > 0, then which one of the following is correct ? 

  2. What are the values of x that satisfy the equation \(\left| {\begin{array}{*{20}{c}} x&0&2\\ {2x}&2&1\\ 1&1&1 \end{array}} \right| + \left| {\begin{array}{*{20}{c}} {3x}&0&2\\ {{x^2}}&2&1\\ 0&1&1 \end{array}} \right| = 0\;?\)

  3. If x + a + b + c = 0, then what is the value of \(\left| {\begin{array}{*{20}{c}} {x + a}&b&c\\ a&{x + b}&c\\ a&b&{x + c} \end{array}} \right|?\)

  4. Which one of the following factors does the expansion of the determinant

    \(\left| {\begin{array}{c} x&y&3\\ {{x^2}}&{5{y^3}}&9\\ {{x^3}}&{10{y^3}}&{27} \end{array}} \right|\) Contain?

  5. If \(u, v\) and \(w\) (all positive) are the \(p^{\text{th}}, q^{\text{th}}\) and \(r^{\text{th}}\) terms of a GP, then the determinant of the matrix is \(\begin{vmatrix} \ln u & p & 1 \\ \ln v & q & 1 \\ \ln w & r & 1 \end{vmatrix}.\)

  6. Let matrix B be the adjoint of a square matrix A, l be the identify matrix of same order as A. If k (≠ 0) is the determinate of the matrix A, then what is AB equal to?

  7. How many matrices of different orders are possible with elements comprising all prime numbers less than 30?

  8. If (a - b) (b - c) (c - a) = 2 and abc = 6, then what is the value of \(\begin{vmatrix}a & b & c \\ a^2 & b^2 & c^2 \\ a^3 & b^3 & c^3 \end{vmatrix}?\)

  9. Under which of the following conditions does the determinant \(\begin{vmatrix}a & b & c \\ b & c & a \\ c & a & b\end{vmatrix}\)  vanish?

    1. a + b + c = 0

    2. a 3+ b 3+ c 3= 3abc

    3. a 2+ b 2+ c 2- ab - bc - ca = 0

    Select the correct answer using the code given below:

  10. If \(a\), \(b\), \(c\) are the sides of a triangle ABC and \(p\) is the perimeter of the triangle, then what is \(\begin{vmatrix} p+c & a & b \\ c & p+a & b \\ c & a & p+b \end{vmatrix}\) equal to?

Important Questions from Determinants

  1. The value of determinant \(\left| {\begin{array}{*{20}{c}} {a - b - c}&{2a}&{2a}\\ {2b}&{b - c - a}&{2b}\\ {2c}&{2c}&{c - a - b} \end{array}} \right|\) is:

  2. If \(\left| {\begin{array}{*{20}{c}} 5&a\\ a&2 \end{array}} \right| = \left| {\begin{array}{*{20}{c}} 2&1\\ 3&2 \end{array}} \right|\), then the values of a are:

  3. The value of the determinant \(\left| {\begin{array}{*{20}{c}} {\sqrt {13} + \sqrt 3 }&{2\sqrt 5 }&{\sqrt 5 }\\ {\sqrt {15} + \sqrt {26} }&5&{\sqrt {10} }\\ {3 + \sqrt {65} }&{\sqrt {15} }&5 \end{array}} \right|\) is

  4. The determinant \(\left| {\begin{array}{*{20}{c}} {xp + y}&x&y\\ {yp + z}&y&z\\ 0&{xp + y}&{yp + z} \end{array}} \right| = 0,\) if

  5. If Δ(a, b, c, α) = 0 for every α > 0, then which one of the following is correct ? 

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