Geometry
Free online geometry video lessons to help students with the formulas, terms and theorems related to triangles, polygons, circles, and other geometric shapes to improve their math problem solving skills while doing their geometry homework and worksheets. Problems presented review concepts such as lines, angles, perimeters, areas, constructions and many more.
Geometry Building Blocks
- Three Undefined Terms: Point, Line, and Plane
- Counterexample
- Writing a Good Definition
- Postulate, Axiom, Conjecture
- Converse
- Line Segments
- Rays
- Parallel and Skew Lines
- Midpoints and Congruent Segments
- Parallel Planes and Lines
- Vertex and Diagonals
- Calculating the Midpoint
- Angles: Types and Labeling
- Using a Protractor
- Angle Bisectors
- Supplementary and Complementary Angles
- Polygons
- Types of Triangles
- Perimeter
- Parts of a Circle
Reasoning, Diagonals, Angles and Parallel Lines
- Inductive Reasoning
- Deductive Reasoning
- Number of Diagonals in a Polygon
- Number of Handshakes at a Party
- Adjacent Angles
- Vertical Angles
- Corresponding Angles
- Alternate Interior Angles
- Alternate Exterior Angles
- Same Side Interior and Same Side Exterior Angles
- Converse of Parallel Lines Theorem
Constructions
- Duplicating a Line Segment
- Duplicating an Angle
- Constructing the Perpendicular Bisector
- Constructing a Perpendicular to a Line
- Constructing an Angle Bisector
- Constructing Parallel Lines
- Constructing Altitudes
- Constructing a Median
- Constructing a Triangle Midsegment
- Point of Concurrency
- Circumscribed and Inscribed Circles and Polygons
- Constructing the Incenter
- Constructing the Circumcenter
- Constructing the Orthocenter
- Constructing the Centroid
- Constructing a Perpendicular at a Point on a Line
Triangles
- Triangle Angle Sum
- Isosceles Triangles
- Triangle Side Inequalities
- Triangle Side and Angle Inequalities
- Remote Interior Angles
- SSS and SAS
- ASA and AAS
- HL
- Why SSA and AAA Don't Work as Congruence Shortcuts
- CPCTC
- Two Column Proofs
- Flowchart Proofs
- Special Isosceles Triangle Properties
Polygons
- Polygon Angle Sum
- Equiangular Polygon Sums
- Exterior Angles of a Polygon
- Kite Properties
- Trapezoid Properties
- Triangle Midsegment Properties
- Trapezoid Midsegment Properties
- Parallelogram Properties
- Trapezoid Arch and Panel Design Problem
- Rhombus Properties
- Rectangle and Square Properties
Circles
- Locus and Definition of a Circle and Sphere
- Central Angles and Intercepted Arcs
- Chords and a Circle's Center
- Radii to Tangents
- Tangent Segments to a Circle
- Inscribed Angles
- Angles in Semicircles and Chords to Tangents
- Cyclic Quadrilaterals and Parallel Lines in Circles
- Circumference
- Arc Length
- Secants
Transformations
- Transformations and Isometries
- Translations
- Reflections
- Rotations
- Compositions of Transformations
- Reflectional Symmetry
- Rotational Symmetry
- Dilations
- Glide Reflections
Area
- Area of Parallelograms
- Area of Triangles
- Area of Trapezoids
- Solving Formulas
- Area of Kites and Rhombuses
- Center and Apothem of Regular Polygons
- Area of Regular Polygons
- Area of Circles
- Area of a Sector
- Area of a Segment
- Area of an Annulus
- Regions Between Circles and Squares
- Surface Area of Prisms
- Surface Area of Cylinders
- Surface Area of Pyramids
- Surface Area of Cones
- Surface Area of Joined Solids
Pythagorean Theorem
- Pythagorean Theorem Proofs
- Square Root Operations
- Using the Pythagorean Theorem to find a Missing Hypotenuse
- Using the Pythagorean Theorem to find a Missing Leg
- Space Diagonals
- Converse of the Pythagorean Theorem
- 45-45-90 Triangles
- 30-60-90 Triangles
- Distance Formula
- Equation of a Circle
- Calculating Coordinates in the Unit Circle
Volume
- 3-D Solid Properties
- Volume of Prisms
- Volume of Cylinders
- Volume of Cones
- Volume of Pyramids
- Solving Equations with Squares and Cubes
- Volume of Spheres
- Surface Area of Spheres
Similarity
- Solving Proportions
- Properties of Similar Polygons
- Similarity Shortcuts
- Similar Triangles in Circles and Right Triangles
- Indirect Measurement
- Proportional Segments Between Parallel Lines
- Corresponding Parts of Similar Triangles
- Angle Bisectors and Opposite Side Ratios
- Similarity and Area Ratios
- Similarity and Volume Ratios