Substitution

Learn and apply substitution using equations, examples, and interpretation.

Lesson 2 of 53 parts Practice Flashcards

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Isolating a Variable

Objective: Explain and use isolating a variable in an Algebra 1 problem.

When one equation expresses y in terms of x, replace y in the other equation with that expression. It reduces two variables to one equation.

Worked examples

Try itExample 1.1: Solve x+y=20 and y=15. Find x.Show answer

5. Substitute the given y into x+y and isolate x. The answer is 5.

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Objective: Explain and use isolating a variable in an Algebra 1 problem.

When one equation expresses y in terms of x, replace y in the other equation with that expression. It reduces two variables to one equation.

Worked examples

Try itExample 1.1: Solve x+y=20 and y=15. Find x.Show answer

5. Substitute the given y into x+y and isolate x. The answer is 5.

Objective: Explain and use solving and back-substitution in an Algebra 1 problem.

After finding one coordinate, substitute it into an original equation to find the other coordinate. A solution is an ordered pair.

Worked examples

Try itExample 2.1: Solve x+y=33 and y=25. Find x.Show answer

8. Substitute the given y into x+y and isolate x. The answer is 8.

Objective: Explain and use checking both equations in an Algebra 1 problem.

An ordered pair is valid only if it satisfies every equation in the system; arithmetic mistakes can be caught by checking both. No, both must hold.

Worked examples

Try itExample 3.1: Solve x+y=46 and y=35. Find x.Show answer

11. Substitute the given y into x+y and isolate x. The answer is 11.

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