In this lesson I will teach you how to prove a quadrilateral is a parallelogram. Of course not every quadrilateral is a parallelogram so it’s important for you to know how to identify and prove a quadrilateral is in fact a parallelogram. Now why would you care if a quadrilateral is or is not a parallelogram? Well one good reason is that once we know a figure is in fact a parallelogram we know a lot about it’s properties and features- this information can really help use solve problems. Hence you want to know methods of proving a quadrilateral is a parallelogram and that’s our focus in this lesson. As you will see in the video we will be using lots of theorems to prove a quadrilateral is a parallelogram. The basic idea is you will look at a quadrilateral and see if it matches the properties of a parallelogram- if it does than you can prove the quadrilateral to be a parallelogram. Don’t forget the previous lessons on how to plan and write a proof as it will help you a lot with this topic. Finally take great notes and keep reviewing course material as the concepts build on each other.

### Video Lessons By Topic

- Absolute Value Inequalities
- Adding and Subtracting Fractions
- Adding and Subtracting Polynomials
- Adding and Subtracting Rational Expressions
- Adding Real Numbers
- Algebra Properties
- Angles
- Arcs and Chords
- Area of Basic Figures
- Best Fitting Lines
- Bisector Theorems
- Circles: Area and Circumference
- Completing The Square
- Complex and Imaginary Numbers
- Composite Functions
- Compound Inequalities
- Compound Interest
- Conditional Statements and Converses
- Congruent Figures
- Deductive and Inductive Reasoning
- Determinants
- Direct and Inverse Variation
- Distributive Property
- Division Rules of Exponents
- Equations-Inequalities-Solutions
- Exponential Growth and Decay
- Factoring Greatest Common Factor
- Factoring Quadratic Trinomials
- Finding The LCD of Rational Expressions
- Formulas and Literal Equations
- Function Operations
- Find The Equation of a Line: Given Slope and a Point
- Find The Equation of a Line: Given Two Points
- Graphing Absolute Value Equations
- Graphing Functions
- Graphing Two Variable Linear Inequalities
- Graphing Lines With One Variable
- Graphing Lines With Two Variables
- Graphing Polynomials
- Graphing Quadratic Equations
- Graphing Quadratic Inequalities
- How to Plan and Write a Proof
- Identity and Inverse Matrices
- Inscribed Circles
- Introduction to Absolute Value
- Introduction to Circles and Tangents
- Introduction to Fractions and Decimals
- Introduction to Functions and Relations
- Introduction to Logarithms
- Introduction to Matrices
- Introduction to Polygons
- Introduction to Polynomials
- Introduction to Quadratic Equations
- Inverse Functions
- Least Common Multiple / Denominator
- Line Segments and Rays
- Linear and Nonlinear Functions
- Linear Inequalities
- Linear Models / Word Problems
- Linear Programming
- Matrix Multiplication
- Matrix Operations
- Medians-Altitudes-Bisectors
- More on Angles and Lines
- Multiplying and Dividing Fractions
- Multiplying and Dividing Rational Expressions
- Multiplying and Dividing Real Numbers
- Multiplying Polynomials
- Multiplying Polynomials Special Cases
- Natural Logarithms
- Negative and Zero Exponents Rules
- Number Operations
- Operations with Radicals
- Order of Operations
- Other Angle Relationships in Circles
- Parallel Lines and Transversals
- Parallelograms
- Percent
- Points-Lines-Planes
- Polynomial Division (Long and Synthetic)
- Product and Power Rules of Exponents
- Properties of Logarithms
- Properties of Parallel and Perpendicular Lines
- Proving Congruent Triangles: ASA and AAS Theorems
- Proving Congruent Triangles: HL Theorem
- Proving Congruent Triangles: SSS and SAS Theorem
- Proving Lines Parallel
- Proving Quadrilaterals are Parallelograms
- Quadratic Equation Word Problems
- Quadrilaterals-Triangles-Midpoints
- Rational Root Theorem (Rational Zero Test)
- Ratios and Proportions
- Ratios and Proportions (Geometry)
- Real Number System
- Reflections
- Remainder and Factor Theorem
- Right Triangle Word Problems
- Rotations and Dilations
- Scientific Notation
- Segment Lengths and Circles
- Similar Polygons
- Similar Right Triangles
- Similar Triangles
- Simplifying by Combining Like Terms
- Simplifying Radicals
- Simplifying Rational Expressions
- Slope Intercept Method
- Solving Absolute Value Equations
- Solving Exponential Equations
- Solving Linear System Word Problems
- Solving Logarithmic Equations
- Solving Multi-Step Equations
- Solving n-Degree Polynomial Equations
- Solving One-Step Equations
- Solving Polynomial Equations by Factoring
- Solving Quadratic Equations by Factoring
- Solving Quadratic Equations by Square Roots
- Solving Radical Equations
- Solving Rational Equations
- Solving Systems by Elimination-Combination Method
- Solving Systems by Graphing
- Solving Systems of Linear Inequalities
- Solving Systems Substitution Method
- Solving Systems using Cramer’s Rule
- Solving Systems using Inverse Matrices
- Solving Two Step Equations
- Special Factoring Rules
- Special Functions
- Special Linear Systems
- Special Quadrilaterals
- Special Right Triangles
- Standard Form of Linear Equations
- Subtracting Real Numbers
- Sum and Difference of Two Cubes
- Surface Area of Basic Figures
- The Discriminant- Type of Roots
- The Distance and Mid-Point Formulas
- The Natural Base e
- The Pythagorean Theorem
- The Quadratic Formula
- The Slope of a Line
- Theorems and Postulates
- Translating Verbal and Algebraic Phrases
- Translations and Guide Reflections
- Trapezoids
- Triangle Inequalities
- Trigonometric Ratios
- Using Point-Slope Intercept
- Using Slope-Intercept Form
- Variables
- Volume of Basic Figures
- XY Intercept Method