# Two Column Proofs

Videos, worksheets, games and activities to help Geometry students learn how to use two column proofs.

A two-column proof consists of a list of statements, and the reasons why those statements are true. The statements are in the left column and the reasons are in the right column. The statements consists of steps toward solving the problem.

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More Geometry Lessons

Two-Column Proof (5 steps) Practice 1
Practice writing a 2 column proof.
Example:
Given AD = 8, BC = 8, $$\overline {BC} \cong \overline {CD}$$
Prove: $$\overline {AD} \cong \overline {CD}$$ Two-Column Proof (7 steps) Practice 2
Practice writing two column proofs.
Example:
Given $$\overline {DE} \cong \overline {FG}$$
Prove: x = 4 Proof Practice (5 steps) Practice 3
Practice writing two column proofs.
Example:
Given MN = PQ
Prove: MP = NQ Practice Proof 4 (Use angle addition postulate)
Practice writing 2 column proofs.
Example:
Given m∠RPS = m∠TPC, m∠TPV = m∠SPT
Prove: m∠RPV = 3(m∠RPS)

How to use the two-column proof to prove the Isosceles Triangle Theorem?
The Isosceles Triangle Theorem states that if two sides of a triangle are congruent, then the angles opposite the sides rae congruent.
How to use the two-column proof to prove the Exterior Angle Theorem?
The Isosceles Triangle Theorem states that the sum of the remote interior angles is equal to the non-adjacent exterior angle.
How to use two column proof to show segments are perpendicular?
Use the SSS, SAS, ASA, AAS postulates.
Using triangle congruency postulates to show that two intersecting segments are perpendicular. (Diagonals of a kite)
How to use two column proof to prove parallel lines?
Given ∠2 ≅ ∠1 ≅ ∠3
Prove: $$\overline {AB} \parallel \overline {CD}$$

Proving a Quadrilateral is a Parallelogram | Geometry Proof
This video geometry lesson proves two parallelogram theorems using the two column proof.
Proof 1: If the diagonals of a quadrilateral bisect each other, then the quadrilateral is a parallelogram.
Proof 2: If both pairs of opposite sides of a quadrilateral are congruent, then the quadrilateral is a parallelogram.
Theorems Used: If both pairs of opposite angles of a quadrilateral are congruent, then the quadrilateral is a parallelogram and If one pair of opposite sides of a quadrilateral is both congruent and parallel, then the quadrilateral is a parallelogram to solve problems. Special Parallelograms - Rhombus and Rectangle Proofs
This video uses the two column method to prove two theorems.
Proof 1: The diagonals of a rectangle are congruent. This amounts to be a triangle proof to use CPCTC.
Proof 2: The diagonals of a rhombus are perpendicular.

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