IXL - Solve a system of equations using substitution (Precalculus practice)

Solve using substitution.

y = ^–10

8x − 3y = 6

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question

Solve using substitution.

x = ^–4

^–2x − 2y = 4

(, )

key idea

To solve using substitution, follow these four steps:

Step 1: Isolate a variable.

Step 2: Plug the result of Step 1 into the other equation and solve for one variable.

Step 3: Plug the result of Step 2 into one of the original equations and solve for the other variable.

Step 4: State the solution.

solution

Use substitution to solve the system of equations:

x = ^–4

^–2x − 2y = 4

Step 1: Isolate a variable.

The variable x is already isolated in the first equation.

Step 2: Plug the result of Step 1 into the other equation and solve for one variable.

Plug x = ^–4 into the other equation, ^–2x − 2y = 4, and find the value of y.

^–2x − 2y

Plug in x = ^–4

^–2(^–4) − 2y

Plug in x = ^–4

Multiply

8 − 2y

Multiply

Subtract 8 from both sides

^–2y

^–4

Subtract 8 from both sides

Divide both sides by ^–2

Step 3: Plug the result of Step 2 into one of the original equations and solve for the other variable.

The first equation already shows that x = ^–4, so it is not necessary to plug in and solve for x.

Step 4: State the solution.

Since x = ^–4 and y = 2, the solution is (^–4, 2).

Looking for more? Try these:

Lesson: Systems of equations

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B.1Solve linear equations

CC.1Evaluate a linear function

Lesson: Systems of equations

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