# 4.12: Solving Linear Systems Using Matrices and Technology

**At Grade**Created by: CK-12

**Practice**Solving Linear Systems Using Matrices and Technology

Customers of the ice cream shop are asking for more sizes, so the shop decides to test out medium and large cones. During its test, the shop sells 24 medium chocolate cones and 32 large chocolate cones. It also sells 40 medium vanilla cones and 60 X-large vanilla cones. The shop's chocolate sales for the day totaled $292 and its vanilla sales totaled $525. How much did the shop charge for a medium cone versus a large cone.

### Guidance

In this concept we will be using the calculator to find the inverse matrix and do matrix multiplication. We have already entered matrices into the calculator and multiplied matrices together on the calculator. To find the inverse of a matrix using the calculator we can call up the matrix by name and use the

Now that we know how to get an inverse using the calculator, let’s look at solving the system. When we translate our system into a matrix equation we have the expression

#### Example A

Use the calculator to find the inverse of the matrix:

**Solution:** First, enter the matrix into the calculator in matrix

#### Example B

Solve the system using matrices on the calculator:

**Solution:** Let

#### Example C

Solve the system using matrices on the calculator:

**Solution:** Let

**Intro Problem Revisit**

Solve the system using matrices on the calculator:

The shop charges $4.50 for a medium cone and $5.75 for a large cone.

### Guided Practice

1. Find the inverse of

Solve the following systems using matrices on the calculator.

2.

3.

#### Answers

1.

The calculator will convert all the values in the matrix to fractions. Press MATH and ENTER to choose

2. Let

3. Let

### Problem Set

Use a calculator to find the inverse of each matrix below.

Solve the systems using matrices and a calculator.

\begin{align*}2x+10y &= 6\\ x+11y &= -3\end{align*}

\begin{align*}-3x+y &= 17\\ 2x-3y &= -23\end{align*}

\begin{align*}10x-5y &= 9\\ 2.5y &= 5x +4\end{align*}

\begin{align*}4x-3y &= -12\\ 7x &= 2y+5\end{align*}

\begin{align*}2x+5y &= 0\\ -4x+10y &= -12\end{align*}

\begin{align*}7x+2y+3z &= -12\\ -8x-y + 4z &= -6\\ -10x+3y+5z &= 1\end{align*}

\begin{align*}2x-4y+11z &= 18\\ -3x+5y-13z &= -25\\ 5x+10y+10z &= 5\end{align*}

\begin{align*}8x+y-4z &= 4\\ -2z-3y+4z &= -7\\ 4 x+5y-8z &= 11\end{align*}

For the following word problems, set up a system of linear equations to solve using matrices.

- A mix of 1 lb almonds and 1.5 lbs cashews sells for $15.00. A mix of 2 lbs almonds and 1 lb cashews sells for $17.00. How much does each nut cost per pound?
- Maria, Rebecca and Sally are selling baked goods for their math club. Maria sold 15 cookies, 20 brownies and 12 cupcakes and raised $23.50. Rebecca sold 22 cookies, 10 brownies and 11 cupcakes and raised $19.85. Sally sold 16 cookies, 5 brownies and 8 cupcakes and raised $13.30. How much did they charge for each type of baked good?
- Justin, Mark and George go to the farmer’s market to buy fruit. Justin buys 2 lbs apples, 3 lbs pears and 1 lb of peaches for $13.24. Mark buys 1 lb apples, 2 lbs pears and 3 lbs peaches for $13.34. George buys 3 lbs apples, 1 lb pears and 2 lbs peaches for $14.04. How much does each fruit cost per pound?

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### Image Attributions

Here you'll learn how to use a graphing calculator to solve systems of linear equations in two and three variables.