CCSS.Math.Content.HSA-REI.C
The standard
Solve systems of equations
Common Core State Standards for Mathematics · High School — Algebra
What this standard means
Students need to find values that make two or more equations true at the same time. They should solve by graphing, substitution, and elimination, and choose a method that fits the system. They also need to interpret the solution as an intersection point or as values that meet all conditions.
Mastery looks like accurate setup, clean algebra, and checking the answer in each original equation. Students often get stuck when signs change during elimination, when substitution creates messy expressions, or when a graph has no clear intersection. They may also miss cases with no solution or infinitely many solutions.
Ways to teach it
- Use two colored strings on grid paper to model linear equations, then mark and label the intersection as the shared solution.
- Ask students to explain which method they would use for a given system and why, before doing any calculations.
- Give a three-question exit ticket with one graphing problem, one substitution problem, and one elimination problem.
- Use a phone plan comparison with two monthly cost equations, then find when the plans cost the same.
Plan a lesson for CCSS.Math.Content.HSA-REI.C
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Related standards
- CCSS.Math.Content.HSA-REI.B
Solve equations and inequalities in one variable
- CCSS.Math.Content.8.EE.C.7
Solve linear equations in one variable.
- CCSS.Math.Content.8.EE.C.8
Analyze and solve pairs of simultaneous linear equations.
- CCSS.Math.Content.8.EE.C.8b
Solve systems of two linear equations in two variables algebraically, and estimate solutions by graphing the equations. Solve simple cases by inspection.