NY Next Generation Math AI-A.REI.1.a

MathGrades 9–12Understand solving equations as a process of reasoning and explain the reasoning.

The Standard

Explain each step when solving a linear or quadratic 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.

New York State Next Generation Mathematics Learning Standards

Teacher's field guide

What This Standard Means

What Students Need to Do

Students explain why each step in solving a linear or quadratic equation preserves equality. They build a logical argument from the assumption that the original equation has a solution.

What Mastery Looks Like

The student names the property or equivalent operation behind each transformation and reaches a correct solution. Substitution checks the result, and the explanation forms a connected argument.

Common Misconceptions

Students may describe steps as moving terms without justifying equality or apply an operation to only one side. They may verify arithmetic without explaining why the method is valid.

How to Assess It

Give 3(x minus 2) equals x plus 8 with a completed solution. Ask students to annotate every step with its equality-preserving reason and verify the result.

Lesson moves

Ways to Teach It

  1. Arrange equation-step cards in a valid order and attach a property card to every transition.

  2. Ask students why subtracting the same expression from both sides preserves the solution set.

  3. Play invalid-step hunt with linear and quadratic solution chains containing one unjustified transformation.

  4. Explain the reasoning in an equation used to find an unknown measurement in a design problem.

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