Determinant of a 3 x 3 matrix

The determinant of a 3 x 3 matrix Formula

We can find the determinant of a matrix in various ways. If we break the smaller 2 x 2 determinant problems as it is easy to handle, we can find the determinant of a 3 x 3 matrix.

Let’s suppose you are given a square matrix C where

C = \(\begin{bmatrix} a & b &c \\ d& e &f \\ g& h &i \end{bmatrix}\)

Let’s calculate the determinant of matrix C,

Det \(\begin{bmatrix} a & b &c \\ d& e &f \\ g& h &i \end{bmatrix}\)

= a. det \(\begin{bmatrix} e & f\\ h & i \end{bmatrix}\) – b.det \(\begin{bmatrix} d & f\\ g & i \end{bmatrix}\) + c . det \(\begin{bmatrix} d & e\\ g & h \end{bmatrix}\)

Few important points on 3x 3 Determinant Matrix

  • The scalar multipliers to a corresponding 2 x 2 matrix have top row elements a, b and c serving to it.
  • The scalar element gets multiplied by 2 x 2 matrix of remaining elements created at the time when vertical and horizontal line segments were drawn through passing through a.
  • This is how we construct the 2 by 2 matrices for scalar multipliers b and c.

The determinant of 3 x 3 Matrix Formula

\(\begin{bmatrix} a & b &c \\ d& e &f \\ g& h &i \end{bmatrix}\) = \(\begin{bmatrix} 2 & -3 &9 \\ 2 & 0 & -1\\ 1& 4 & 5 \end{bmatrix}\)

Determinant of a 3X3 Matrix formula
Determinant of a 3 X 3 matrix

Determinant of the 3 x 3 matrix examples:

Example 1:

Calculate the determinant of the 3 x 3 matrix.

\(\begin{bmatrix} 2 & -3 &9 \\ 2 & 0 & -1\\ 1& 4 & 5 \end{bmatrix}\)

Solution: Let’s find the correspondence between the generic elements in the formula and elements of real problem.

\(\begin{bmatrix} a & b &c \\ d& e &f \\ g& h &i \end{bmatrix}\) = \(\begin{bmatrix} 2 & -3 &9 \\ 2 & 0 & -1\\ 1& 4 & 5 \end{bmatrix}\)

Use the 3 x 3 determinant formula:

Applying the formula,

Use the 3 x 3 determinant formula

= 2[ 0 – (-4)] + 3 [10 – (-1)] + 3 [10 – (-1)] +1 [8-0]

= 2 (0+4) +3 (10 +1) + 1(8)

= 2(4) +3(11) + 8

= 8+33+8

= 49

Example 2:

Calculate the determinant of the 3 x 3 matrix.

\(\begin{bmatrix} 1 & 3 &2 \\ -3 & -1 & -3\\ 2& 3 & 1 \end{bmatrix}\)

Solution: Let’s find the correspondence between the generic elements in the formula and elements of real problem.

\(\begin{bmatrix} a & b &c \\ d& e &f \\ g& h &i \end{bmatrix}\) = \(\begin{bmatrix} 1 & 3 &2 \\ -3 & -1 & -3\\ 2& 3 & 1 \end{bmatrix}\)

Use the 3 x 3 determinant formula:

Determinant of a 3x3 matrix-1

= 1[ -1 – (-9)] – 3 [-3 – (-6)] + 2 [-9 – (-2)]

= 1 (-1+9) -3 (-3 +6) + 2(-9 + 2)

= 1(8) -3(3) +2(-7)

= 8 -9-14

= -15

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Practise This Question

The figure can be formed in the shape of a die.

 

 

 

Find the value of B?