How to Solve Matrix Equations

How to Solve Matrix Equations

 Read,2 minutes

What is a Matrix Equation?

A matrix equation has the form \(AX \ = \ B\), where \(A\) is the coefficient matrix, X is the column matrix of variables, and \(B\) is the column matrix of constants on the right side of the equations in a system.

Solving Matrix Equation?

Let's figure out what \(X\) is in the equation \(AX \ = \ B\). We did this by multiplying each side of the equation by (\(A^{-1}\)). (the inverse of \(A\))

\(AX \ = \ B \ ⇒ \ A^{-1} \ (AX) \ = \ A^{-1} \ B\)

We know that \(A^{-1} A\) equals \(I\), where \(I\) is the same-order identity matrix as \(A\). So,

\(IX \ = \ A^{-1} \ B\)

Also we know that: \(IX \ = \ X\). So,

\(X \ = \ A^{-1} \ B\)

The answer to the matrix equation is found here. This is also called the "inverse matrix equation," and the way to solve a set of equations by using the above formula is called the "inverse matrix method." So, here are the steps to use matrices to solve a set of equations:

  • Put the system into the form of the matrix equation \(AX \ = \ B\).
  • Find the Inverse of \(A\).
  • To get the answer, multiply it by the constant matrix \(B\). i.e., \(X \ = \ A^{-1}B\).

Free printable Worksheets

Exercises for Solving Matrix Equations

1) Find the answer: \(X \ + \ \begin{bmatrix} 2 & -5 \\\ 7 & 3 \end{bmatrix} \ = \ \begin{bmatrix} -4 & -2 \\\ 4 & -9 \end{bmatrix}\)

2) Find the answer: \(X \ - \ \begin{bmatrix} 11 & 3 \\\ -5 & 8 \end{bmatrix} \ = \ \begin{bmatrix} 13 & 21 \\\ -7 & 6 \end{bmatrix}\)

3) Find the answer: \(2Y \ + \ \begin{bmatrix} 9 & -23 \\\ -15 & -7 \end{bmatrix} \ = \ \begin{bmatrix} -8 & -27 \\\ 13 & 3 \end{bmatrix}\)

4) Find the answer: \(2Y \ - \ \begin{bmatrix} -15 & 21 \\\ 19 & -17 \end{bmatrix} \ = \ \begin{bmatrix} 9 & 16 \\\ -12 & 7 \end{bmatrix}\)

5) Find the answer: \(2X \ + \ \begin{bmatrix} -7 & 11 \\\ -7 & -7 \end{bmatrix} \ = \ \begin{bmatrix} 15 & -29 \\\ 17 & -11 \end{bmatrix}\)

6) Find the answer: \(2X \ + \ \begin{bmatrix} 19 & -20 & 8 \end{bmatrix} \ = \ \begin{bmatrix} 25 & -31 & -12 \end{bmatrix}\)

7) Find the answer: \(X \times \begin{bmatrix} 2 & -4 \\\ 1 & 3 \end{bmatrix} \ = \ \begin{bmatrix} 3 & -1 \\\ 2 & -3 \end{bmatrix}\)

8) Find the answer: \(X \times \begin{bmatrix} 5 & 1 \\\ 2 & -3 \end{bmatrix} \ = \ \begin{bmatrix} 8 & 6 \\\ 9 & 12 \end{bmatrix}\)

9) Find the answer: \(-3X \ = \ \begin{bmatrix} -18 & 33 & -69 \end{bmatrix}\)

10) Find the answer: \(7 \ Y \ = \ \begin{bmatrix} 70 & 42 & -56 \end{bmatrix}\)

 

1) Find the answer: \(X \ + \ \begin{bmatrix} 2 & -5 \\\ 7 & 3 \end{bmatrix} \ = \ \begin{bmatrix} -4 & -2 \\\ 4 & -9 \end{bmatrix}\)

\(\color{red}{X \ = \ \begin{bmatrix} -4 & -2 \\\ 4 & -9 \end{bmatrix} \ - \ \begin{bmatrix} 2 & -5 \\\ 7 & 3 \end{bmatrix} \ = \ \begin{bmatrix} -6 & 3 \\\ -3 & -12 \end{bmatrix}}\)

2) Find the answer: \(X \ - \ \begin{bmatrix} 11 & 3 \\\ -5 & 8 \end{bmatrix} \ = \ \begin{bmatrix} 13 & 21 \\\ -7 & 6 \end{bmatrix}\)

\(\color{red}{X \ = \ \begin{bmatrix} 11 & 3 \\\ -5 & 8 \end{bmatrix} \ + \ \begin{bmatrix} 13 & 21 \\\ -7 & 6 \end{bmatrix} \ = \ \begin{bmatrix} 24 & 24 \\\ -12 & 14 \end{bmatrix}}\)

3) Find the answer: \(2Y \ + \ \begin{bmatrix} 9 & -23 \\\ -15 & -7 \end{bmatrix} \ = \ \begin{bmatrix} -8 & -27 \\\ 13 & 3 \end{bmatrix}\)

\(\color{red}{2Y \ = \ \begin{bmatrix} -8 & -27 \\\ 13 & 3 \end{bmatrix} \ - \ \begin{bmatrix} 9 & -23 \\\ -15 & -7 \end{bmatrix} \ = \ \begin{bmatrix} -17 & -4 \\\ 28 & 10 \end{bmatrix} \ ⇒ \ Y \ = \ \begin{bmatrix} -8.5 & -2 \\\ 14 & 5 \end{bmatrix}}\)

4) Find the answer: \(2Y \ - \ \begin{bmatrix} -15 & 21 \\\ 19 & -17 \end{bmatrix} \ = \ \begin{bmatrix} 9 & 16 \\\ -12 & 7 \end{bmatrix}\)

\(\color{red}{2Y \ = \ \begin{bmatrix} -15 & 21 \\\ 19 & -17 \end{bmatrix} \ + \ \begin{bmatrix} 9 & 16 \\\ -12 & 7 \end{bmatrix} \ = \ \begin{bmatrix} -6 & 37 \\\ 7 & -10 \end{bmatrix} \ ⇒ \ Y \ = \ \begin{bmatrix} -3 & 18.5 \\\ 3.5 & -5 \end{bmatrix}}\)

5) Find the answer: \(2X \ + \ \begin{bmatrix} -7 & 11 \\\ -7 & -7 \end{bmatrix} \ = \ \begin{bmatrix} 15 & -29 \\\ 17 & -11 \end{bmatrix}\)

\(\color{red}{2X \ = \ \begin{bmatrix} 15 & -29 \\\ 17 & -11 \end{bmatrix} \ - \ \begin{bmatrix} -7 & 11 \\\ -7 & -7 \end{bmatrix} \ = \ \begin{bmatrix} 22 & -40 \\\ 24 & -4 \end{bmatrix} \ ⇒ \ X \ = \ \begin{bmatrix} 11 & -20 \\\ 12 & -2 \end{bmatrix}}\)

6) Find the answer: \(2X \ + \ \begin{bmatrix} 19 & -20 & 8 \end{bmatrix} \ = \ \begin{bmatrix} 25 & -31 & -12 \end{bmatrix}\)

\(\color{red}{2X \ = \ \begin{bmatrix} 25 & -31 & -12 \end{bmatrix} \ - \ \begin{bmatrix} 19 & -20 & 8 \end{bmatrix} \ = \ \begin{bmatrix} 6 & -11 & -20 \end{bmatrix}}\) \(\color{red}{ ⇒ \ X \ = \ \begin{bmatrix} 3 & -5.5 & -10 \end{bmatrix}}\)

7) Find the answer: \(X \times \begin{bmatrix} 2 & -4 \\\ 1 & 3 \end{bmatrix} \ = \ \begin{bmatrix} 3 & -1 \\\ 2 & -3 \end{bmatrix}\)

\(\color{red}{X \times \begin{bmatrix} 2 & -4 \\\ 1 & 3 \end{bmatrix} \ = \ \begin{bmatrix} 3 & -1 \\\ 2 & -3 \end{bmatrix} \ ⇒ \ X \ = \ \begin{bmatrix} 3 & -1 \\\ 2 & -3 \end{bmatrix} \times \begin{bmatrix} 2 & -4 \\\ 1 & 3 \end{bmatrix}^{-1}}\) \(\color{red}{ \ = \ \begin{bmatrix} 3 & -1 \\\ 2 & -3 \end{bmatrix} \times \begin{bmatrix} \frac{3}{10} & \frac{2}{5} \\\ -\frac{1}{10} & \frac{1}{5} \end{bmatrix}= \ \begin{bmatrix} \frac{17}{10} & -\frac{3}{2} \\\ \frac{1}{10} & -\frac{1}{2} \end{bmatrix}}\)

8) Find the answer: \(X \times \begin{bmatrix} 5 & 1 \\\ 2 & -3 \end{bmatrix} \ = \ \begin{bmatrix} 8 & 6 \\\ 9 & 12 \end{bmatrix}\)

\(\color{red}{X \times \begin{bmatrix} 5 & 1 \\\ 2 & -3 \end{bmatrix} \ = \ \begin{bmatrix} 8 & 6 \\\ 9 & 12 \end{bmatrix} \ ⇒ \ X \ = \ \begin{bmatrix} 8 & 6 \\\ 9 & 12 \end{bmatrix} \times \begin{bmatrix} 5 & 1 \\\ 2 & -3 \end{bmatrix}^{-1}}\) \(\color{red}{ \ = \ \begin{bmatrix} 8 & 6 \\\ 9 & 12 \end{bmatrix} \times \begin{bmatrix} \frac{3}{17} & \frac{1}{17} \\\ \frac{2}{17} & -\frac{5}{17} \end{bmatrix}= \ \begin{bmatrix} \frac{33}{17} & \frac{30}{17} \\\ -\frac{29}{17} & -\frac{48}{17} \end{bmatrix}}\)

9) Find the answer: \(-3X \ = \ \begin{bmatrix} -18 & 33 & -69 \end{bmatrix}\)

\(\color{red}{-3X \ = \ \begin{bmatrix} -18 & 33 & -69 \end{bmatrix} \ ⇒ \ X \ = \ \begin{bmatrix} 6 & -11 & 23 \end{bmatrix}}\)

10) Find the answer: \(7 \ Y \ = \ \begin{bmatrix} 70 & 42 & -56 \end{bmatrix}\)

\(\color{red}{7 \ Y \ = \ \begin{bmatrix} 70 & 42 & -56 \end{bmatrix} \ ⇒ \ Y \ = \ \begin{bmatrix} 10 & 6 & -8 \end{bmatrix}}\)

Matrix Equations Practice Quiz