Proofs Teacher Resources

In this geometry worksheet, 10th graders solve problems involving quadrilaterals using the angle sum of quadrilaterals. They solve for linear pairs, opposite angle theorem and triangular angles. There are 5 questions.

In this postulates and theorems worksheet, students explore a concept map containing information about angles and sides, alternate interior angles, and diagonals of a parallelogram.  They use the concept map to prove theorems...

Students explore the concept of polygon properties. In this polygon properties lesson, students draw polygons with different numbers of sides such as pentagons, octagons, hexagons, etc. Students identify different geometric shapes in the...

Proof by contradiction that if two lines cut by a transversal create congruent corresponding angles then the lines are parallel. [5:18]

Explains how to determine the measures of all the angles formed when parallel lines are cut by a transversal based on the measure of one angle. Explains how to use corresponding congruent angles to determine if lines cut by a transversal...

Proof by contradiction that corresponding angle equivalence implies parallel lines.

Demonstrates solutions to problems #7-10 of California Geometry released state test questions. Problems address understanding of congruent angle pairs when parallel lines are cut by a transversal, counterexamples, and properties of the...

Proof that the sum of the angles in a triangle is 180 using the relationship of angles formed when parallel lines are cut by a transversal. This video also appears in the Geometry: Triangles strand. [6:31]

This investigation uses Cabri Jr. and a cleaver rotation of a triangle to "prove" that the angles in a triangle add up to 180. This could be used to reinforce triangles and paralled lines as well as introduce the concept of rotating an...

This video tutorial demonstrates how to prove that the opposite angles of a parallelogram are congruent based on knowledge of the special angles created when parallel lines are cut by a transversal. [4:08]

Demonstrates how to prove that the diagonals of a parallelogram bisect each other based on knowledge of the special angles created when parallel lines are cut by a transversal and the triangle congruency postulates. [9:06]

Demonstrates how to prove that the opposite sides of a parallelogram are congruent based on knowledge of the special angles created when parallel lines are cut by a transversal and the triangle congruency postulates. [8:30]

Video lesson explains angles, lines, and transversals. [9:33]

Proving that vertical angles are equal

This video tutorial demonstrates solutions to problems #51-55 of the California Geometry released state test questions. Problems address proving and using the Pythagorean theorem and compass constructions. [12:35]