CCSS.Math.Content.HSA-REI.A.1
The standard
Explain each step in solving a simple equation as following from the equality of numbers asserted at the previous step, starting from the assumption that the original equation has a solution. Construct a viable argument to justify a solution method.
Common Core State Standards for Mathematics
What this standard means
Students need to solve equations and explain why each move is allowed. They should connect every step to keeping both sides equal, not just say “move it over” or “do the opposite.” They also need to start with the idea that a solution exists, then show how their steps lead to it.
Mastery looks like a clear solution with reasons beside each line, such as adding the same number to both sides or dividing both sides by a nonzero number. Students often get stuck using shortcuts without meaning, skipping steps, or making sign errors they cannot justify.
Ways to teach it
- Give pairs equation strips and reason cards, then have them match each algebra step to its legal justification.
- Ask students to write a two-column solution for 3x - 7 = 11, with every line explained in words.
- Use an exit ticket with one solved equation containing a bad step, and ask students to find and correct it.
- Connect to balancing a scale by using counters or weights to show why the same operation must happen on both sides.
Plan a lesson for CCSS.Math.Content.HSA-REI.A.1
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Related standards
- CCSS.Math.Content.HSA-REI.A.2
Solve simple rational and radical equations in one variable, and give examples showing how extraneous solutions may arise.
- CCSS.Math.Content.HSA-REI.A
Understand solving equations as a process of reasoning and explain the reasoning
- CCSS.Math.Content.6.EE.B
Reason about and solve one-variable equations and inequalities.
- CCSS.Math.Content.6.EE.B.5
Understand solving an equation or inequality as a process of answering a question: which values from a specified set, if any, make the equation or inequality tr...