Linear Algebra Examples

$[\begin{array}{c} 1 & 2 & 3 \\ x & y & z \end{array}] [\begin{array}{c} 1 & x \\ 2 & y \\ 3 & z \end{array}]$

Step 1

Multiply $[\begin{array}{c} 1 & 2 & 3 \\ x & y & z \end{array}] [\begin{array}{c} 1 & x \\ 2 & y \\ 3 & z \end{array}]$ .

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Step 1.1

Two matrices can be multiplied if and only if the number of columns in the first matrix is equal to the number of rows in the second matrix. In this case, the first matrix is $2 \times 3$ and the second matrix is $3 \times 2$ .

Step 1.2

Multiply each row in the first matrix by each column in the second matrix.

$[\begin{array}{c} 1 \cdot 1 + 2 \cdot 2 + 3 \cdot 3 & 1 x + 2 y + 3 z \\ x \cdot 1 + y \cdot 2 + z \cdot 3 & x \cdot x + y \cdot y + z \cdot z \end{array}]$

Step 1.3

Simplify each element of the matrix by multiplying out all the expressions.

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Step 1.3.1

Multiply $x$ by $x$ .

$[\begin{array}{c} 14 & x + 2 y + 3 z \\ x + 2 y + 3 z & x^{2} + y \cdot y + z \cdot z \end{array}]$

Step 1.3.2

Multiply $y$ by $y$ .

$[\begin{array}{c} 14 & x + 2 y + 3 z \\ x + 2 y + 3 z & x^{2} + y^{2} + z \cdot z \end{array}]$

Step 1.3.3

Multiply $z$ by $z$ .

$[\begin{array}{c} 14 & x + 2 y + 3 z \\ x + 2 y + 3 z & x^{2} + y^{2} + z^{2} \end{array}]$

Step 2

The determinant of a $2 \times 2$ matrix can be found using the formula $| \begin{array}{c} a & b \\ c & d \end{array} | = a d - c b$ .

$14 (x^{2} + y^{2} + z^{2}) - (x + 2 y + 3 z) (x + 2 y + 3 z)$

Step 3

Simplify the determinant.

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Step 3.1

Simplify each term.

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Step 3.1.1

Apply the distributive property.

$14 x^{2} + 14 y^{2} + 14 z^{2} - (x + 2 y + 3 z) (x + 2 y + 3 z)$

Step 3.1.2

Apply the distributive property.

$14 x^{2} + 14 y^{2} + 14 z^{2} + (- x - (2 y) - (3 z)) (x + 2 y + 3 z)$

Step 3.1.3

Simplify.

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Step 3.1.3.1

Multiply $2$ by $- 1$ .

$14 x^{2} + 14 y^{2} + 14 z^{2} + (- x - 2 y - (3 z)) (x + 2 y + 3 z)$

Step 3.1.3.2

Multiply $3$ by $- 1$ .

$14 x^{2} + 14 y^{2} + 14 z^{2} + (- x - 2 y - 3 z) (x + 2 y + 3 z)$

Step 3.1.4

Expand $(- x - 2 y - 3 z) (x + 2 y + 3 z)$ by multiplying each term in the first expression by each term in the second expression.

$14 x^{2} + 14 y^{2} + 14 z^{2} - x \cdot x - x (2 y) - x (3 z) - 2 y x - 2 y (2 y) - 2 y (3 z) - 3 z x - 3 z (2 y) - 3 z (3 z)$

Step 3.1.5

Simplify each term.

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Step 3.1.5.1

Multiply $x$ by $x$ by adding the exponents.

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Step 3.1.5.1.1

Move $x$ .

$14 x^{2} + 14 y^{2} + 14 z^{2} - (x \cdot x) - x (2 y) - x (3 z) - 2 y x - 2 y (2 y) - 2 y (3 z) - 3 z x - 3 z (2 y) - 3 z (3 z)$

Step 3.1.5.1.2

Multiply $x$ by $x$ .

$14 x^{2} + 14 y^{2} + 14 z^{2} - x^{2} - x (2 y) - x (3 z) - 2 y x - 2 y (2 y) - 2 y (3 z) - 3 z x - 3 z (2 y) - 3 z (3 z)$

Step 3.1.5.2

Rewrite using the commutative property of multiplication.

$14 x^{2} + 14 y^{2} + 14 z^{2} - x^{2} - 1 \cdot 2 x y - x (3 z) - 2 y x - 2 y (2 y) - 2 y (3 z) - 3 z x - 3 z (2 y) - 3 z (3 z)$

Step 3.1.5.3

Multiply $- 1$ by $2$ .

$14 x^{2} + 14 y^{2} + 14 z^{2} - x^{2} - 2 x y - x (3 z) - 2 y x - 2 y (2 y) - 2 y (3 z) - 3 z x - 3 z (2 y) - 3 z (3 z)$

Step 3.1.5.4

Rewrite using the commutative property of multiplication.

$14 x^{2} + 14 y^{2} + 14 z^{2} - x^{2} - 2 x y - 1 \cdot 3 x z - 2 y x - 2 y (2 y) - 2 y (3 z) - 3 z x - 3 z (2 y) - 3 z (3 z)$

Step 3.1.5.5

Multiply $- 1$ by $3$ .

$14 x^{2} + 14 y^{2} + 14 z^{2} - x^{2} - 2 x y - 3 x z - 2 y x - 2 y (2 y) - 2 y (3 z) - 3 z x - 3 z (2 y) - 3 z (3 z)$

Step 3.1.5.6

Rewrite using the commutative property of multiplication.

$14 x^{2} + 14 y^{2} + 14 z^{2} - x^{2} - 2 x y - 3 x z - 2 y x - 2 \cdot 2 y \cdot y - 2 y (3 z) - 3 z x - 3 z (2 y) - 3 z (3 z)$

Step 3.1.5.7

Multiply $y$ by $y$ by adding the exponents.

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Step 3.1.5.7.1

Move $y$ .

$14 x^{2} + 14 y^{2} + 14 z^{2} - x^{2} - 2 x y - 3 x z - 2 y x - 2 \cdot 2 (y \cdot y) - 2 y (3 z) - 3 z x - 3 z (2 y) - 3 z (3 z)$

Step 3.1.5.7.2

Multiply $y$ by $y$ .

$14 x^{2} + 14 y^{2} + 14 z^{2} - x^{2} - 2 x y - 3 x z - 2 y x - 2 \cdot 2 y^{2} - 2 y (3 z) - 3 z x - 3 z (2 y) - 3 z (3 z)$

Step 3.1.5.8

Multiply $- 2$ by $2$ .

$14 x^{2} + 14 y^{2} + 14 z^{2} - x^{2} - 2 x y - 3 x z - 2 y x - 4 y^{2} - 2 y (3 z) - 3 z x - 3 z (2 y) - 3 z (3 z)$

Step 3.1.5.9

Rewrite using the commutative property of multiplication.

$14 x^{2} + 14 y^{2} + 14 z^{2} - x^{2} - 2 x y - 3 x z - 2 y x - 4 y^{2} - 2 \cdot 3 y z - 3 z x - 3 z (2 y) - 3 z (3 z)$

Step 3.1.5.10

Multiply $- 2$ by $3$ .

$14 x^{2} + 14 y^{2} + 14 z^{2} - x^{2} - 2 x y - 3 x z - 2 y x - 4 y^{2} - 6 y z - 3 z x - 3 z (2 y) - 3 z (3 z)$

Step 3.1.5.11

Rewrite using the commutative property of multiplication.

$14 x^{2} + 14 y^{2} + 14 z^{2} - x^{2} - 2 x y - 3 x z - 2 y x - 4 y^{2} - 6 y z - 3 z x - 3 \cdot 2 z y - 3 z (3 z)$

Step 3.1.5.12

Multiply $- 3$ by $2$ .

$14 x^{2} + 14 y^{2} + 14 z^{2} - x^{2} - 2 x y - 3 x z - 2 y x - 4 y^{2} - 6 y z - 3 z x - 6 z y - 3 z (3 z)$

Step 3.1.5.13

Rewrite using the commutative property of multiplication.

$14 x^{2} + 14 y^{2} + 14 z^{2} - x^{2} - 2 x y - 3 x z - 2 y x - 4 y^{2} - 6 y z - 3 z x - 6 z y - 3 \cdot 3 z \cdot z$

Step 3.1.5.14

Multiply $z$ by $z$ by adding the exponents.

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Step 3.1.5.14.1

Move $z$ .

$14 x^{2} + 14 y^{2} + 14 z^{2} - x^{2} - 2 x y - 3 x z - 2 y x - 4 y^{2} - 6 y z - 3 z x - 6 z y - 3 \cdot 3 (z \cdot z)$

Step 3.1.5.14.2

Multiply $z$ by $z$ .

$14 x^{2} + 14 y^{2} + 14 z^{2} - x^{2} - 2 x y - 3 x z - 2 y x - 4 y^{2} - 6 y z - 3 z x - 6 z y - 3 \cdot 3 z^{2}$

Step 3.1.5.15

Multiply $- 3$ by $3$ .

$14 x^{2} + 14 y^{2} + 14 z^{2} - x^{2} - 2 x y - 3 x z - 2 y x - 4 y^{2} - 6 y z - 3 z x - 6 z y - 9 z^{2}$

Step 3.1.6

Subtract $2 y x$ from $- 2 x y$ .

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Step 3.1.6.1

Move $y$ .

$14 x^{2} + 14 y^{2} + 14 z^{2} - x^{2} - 2 x y - 2 x y - 3 x z - 4 y^{2} - 6 y z - 3 z x - 6 z y - 9 z^{2}$

Step 3.1.6.2

Subtract $2 x y$ from $- 2 x y$ .

$14 x^{2} + 14 y^{2} + 14 z^{2} - x^{2} - 4 x y - 3 x z - 4 y^{2} - 6 y z - 3 z x - 6 z y - 9 z^{2}$

Step 3.1.7

Subtract $3 z x$ from $- 3 x z$ .

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Step 3.1.7.1

Move $z$ .

$14 x^{2} + 14 y^{2} + 14 z^{2} - x^{2} - 4 x y - 4 y^{2} - 6 y z - 3 x z - 3 x z - 6 z y - 9 z^{2}$

Step 3.1.7.2

Subtract $3 x z$ from $- 3 x z$ .

$14 x^{2} + 14 y^{2} + 14 z^{2} - x^{2} - 4 x y - 4 y^{2} - 6 y z - 6 x z - 6 z y - 9 z^{2}$

Step 3.1.8

Subtract $6 z y$ from $- 6 y z$ .

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Step 3.1.8.1

Move $z$ .

$14 x^{2} + 14 y^{2} + 14 z^{2} - x^{2} - 4 x y - 4 y^{2} - 6 y z - 6 y z - 6 x z - 9 z^{2}$

Step 3.1.8.2

Subtract $6 y z$ from $- 6 y z$ .

$14 x^{2} + 14 y^{2} + 14 z^{2} - x^{2} - 4 x y - 4 y^{2} - 12 y z - 6 x z - 9 z^{2}$

Step 3.2

Subtract $x^{2}$ from $14 x^{2}$ .

$13 x^{2} + 14 y^{2} + 14 z^{2} - 4 x y - 4 y^{2} - 12 y z - 6 x z - 9 z^{2}$

Step 3.3

Subtract $4 y^{2}$ from $14 y^{2}$ .

$13 x^{2} + 10 y^{2} + 14 z^{2} - 4 x y - 12 y z - 6 x z - 9 z^{2}$

Step 3.4

Subtract $9 z^{2}$ from $14 z^{2}$ .

$13 x^{2} + 10 y^{2} + 5 z^{2} - 4 x y - 12 y z - 6 x z$