School Improvement in Maryland

Lesson Plan: Lesson plans were written by Maryland mathematics educators and could be used when teaching the concepts.

Goal 2 Geometry, Measurement, And Reasoning

Expectation 2.2 The student will apply geometric properties and relationships to solve problems using tools and technology when appropriate.

Indicator 2.2.3 The student will use inductive or deductive reasoning.

Lesson Content

Justification in Proof


Students will be able to identify and apply properties of equality and properties of congruence, and validate properties of geometric figures and explain the processes used.

Approximate Time

50-minute lesson

Prerequisite Concepts Needed

Students will need to be able to interpret and analyze conditional statements.

Materials Needed

Lesson Structure

    Essential Questions

    How can deductive reasoning be used to validate conjectures?
    What methods can be used to organize a deductive argument?

    Warm-Up/Opening Activity

    Solve a two-step equation.

    Development of Ideas

    Overhead: What is a Proof?
    Justify the steps to solve an equation using the properties of equality.
    Identify and apply the properties of equality and the properties of congruence to geometric figures.
    Worksheet: Justification Using Properties of Equality and Congruence


    Compare and contrast inductive and deductive reasoning.
    Worksheet: Comparison of Inductive and Deductive Reasoning