**Related Pages**

Geometry Proofs

Geometry Lessons

In these lessons, we will learn how to use two column proofs for geometric 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.

The following figure gives a Two-column Proof for the Isosceles Triangle Theorem. Scroll down
the page for more examples and solutions.

How To Use The Two-Column Proof To Prove The Isosceles Triangle Theorem? Click here

How To Use The Two-Column Proof To Prove The Exterior Angle Theorem? Click here

How To Use Two Column Proof To Show Segments Are Perpendicular? Click here

How To Use Two Column Proof To Prove Parallel Lines? Click here

How To Use Two Column Proof To Prove a Quadrilateral is a Parallelogram? Click here

Practice writing a 2 column proof.

**Example:**

Given AD = 8, BC = 8, B̅C̅ ≅ C̅D̅

Prove: A̅D̅ ≅ C̅D̅

Practice writing two column proofs.

**Example:**

Given D̅E̅ ≅ F̅G̅

Prove: x = 4

Practice writing two column proofs.

**Example:**

Given MN = PQ

Prove: MP = NQ

Practice writing 2 column proofs.

**Example:**

Given m∠RPS = m∠TPC, m∠TPV = m∠SPT

Prove: m∠RPV = 3(m∠RPS)

The Isosceles Triangle Theorem states that if two sides of a triangle are congruent, then the angles opposite the sides are congruent.

The Exterior Angle Theorem states that the sum of the remote interior angles is equal to the non-adjacent exterior angle.

Use the SSS, SAS, ASA, AAS postulates.

Using triangle congruency postulates to show that two intersecting segments are perpendicular. (Diagonals of a kite)

Given ∠2 ≅ ∠1 ≅ ∠3

Prove: A̅B̅ || C̅D̅

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.

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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