Geometry (all content)
Learn geometry—angles, shapes, transformations, proofs, and more.
17 units347 videos35 hours
Learn it live with a class on Puzzicle · Teachers: use it with your class
Unit 1: Lines
Lines, line segments, and rays
Measuring segments
Parallel and perpendicular
Points, lines, & planes
Geometric definitions
The golden ratio
Unit 2: Angles
Angle introduction
Measuring angles
Constructing angles
Angles in circles
Angle types
Vertical, complementary, and supplementary angles
Angles between intersecting lines
Angles, parallel lines, & transversals ✓ Check-ins7:07
Parallel & perpendicular lines ✓ Check-ins3:35
Missing angles with a transversal ✓ Check-ins2:16
Parallel lines & corresponding angles proof ✓ Check-ins ✎ Fixed a slip5:18
Missing angles (CA geometry) ✓ Check-ins10:58
Proving angles are congruent ✓ Check-ins ✎ Fixed a slip4:53
Proofs with transformations ✓ Check-ins8:45
Sal's old angle videos
Intro to angles (old) ✓ Check-ins9:55
Angles (part 2) ✓ Check-ins9:04
Angles (part 3) ✓ Check-ins9:47
Angles formed between transversals and parallel lines ✓ Check-ins7:53
Angles of parallel lines 2 ✓ Check-ins5:15
The angle game ✓ Check-ins ✎ Fixed a slip9:01
The angle game (part 2) ✓ Check-ins ✎ Fixed a slip9:49
Acute, right, & obtuse angles ✓ Check-ins5:32
Unit 3: Shapes
Properties of shapes
Equal parts of shapes
Classifying geometric shapes
Curves and polygons
Angles with polygons
Geometric solids (3D shapes)
Unit 4: Triangles
Triangle types
Triangle angles
Angles in a triangle sum to 180° proof ✓ Check-ins4:28
Triangle exterior angle example ✓ Check-ins6:03
Worked example: Triangle angles (intersecting lines) ✓ Check-ins4:55
Worked example: Triangle angles (diagram) ✓ Check-ins5:42
Triangle angle challenge problem ✓ Check-ins8:37
Triangle angle challenge problem 2 ✓ Check-ins6:05
Triangle inequality theorem
Perpendicular bisectors
Angle bisectors
Medians & centroids
Triangle medians & centroids ✓ Check-ins ✎ Fixed a slip8:59
Triangle medians and centroids (2D proof) ✓ Check-ins15:15
Dividing triangles with medians ✓ Check-ins7:46
Exploring medial triangles ✓ Check-ins11:33
Centroid & median proof ✓ Check-ins ✎ Fixed a slip6:56
Median, centroid example ✓ Check-ins9:00
Altitudes
Unit 5: Quadrilaterals
Quadrilateral types
Quadrilateral proofs & angles
Proof: Opposite sides of a parallelogram ✓ Check-ins8:30
Proof: Diagonals of a parallelogram ✓ Check-ins9:06
Proof: Opposite angles of a parallelogram ✓ Check-ins4:08
Proof: Rhombus diagonals are perpendicular bisectors ✓ Check-ins4:04
Whether a special quadrilateral can exist ✓ Check-ins5:08
Rhombus diagonals ✓ Check-ins4:38
Unit 6: Coordinate plane
Coordinate plane: quadrant 1
Coordinate plane: 4 quadrants
Quadrants on the coordinate plane
Reflecting points on coordinate plane
Quadrilaterals on the coordinate plane
Drawing polygons in the coordinate plane
Unit 7: Area and perimeter
Count unit squares to find area
Area of rectangles
Perimeter
Perimeter: introduction ✓ Check-ins3:21
Perimeter of a shape ✓ Check-ins2:03
Finding perimeter when a side length is missing ✓ Check-ins3:31
Finding missing side length when given perimeter ✓ Check-ins4:55
Perimeter & area ✓ Check-ins ✎ Fixed a slip8:25
Perimeter and unit conversion ✓ Check-ins6:13
Applying the metric system to perimeter ✓ Check-ins5:43
Area of parallelograms
Area of shapes on grids
Area of trapezoids & composite figures
Area and circumference of circles
Unit 8: Volume and surface area
Volume of rectangular prisms
Volume with fractions
Surface area
Volume of cones, cylinders, and spheres
Surface and volume density
Cross sections of 3D objects
Koch snowflake fractal
Unit 9: Pythagorean theorem
Pythagorean theorem
Pythagorean theorem application
Pythagorean theorem and distance between points
Unit 10: Transformations
Introduction to rigid transformations
Translations
Rotations
Reflections
Dilations
Properties and definitions of transformations
Symmetry
Old transformations videos
Performing translations (old) ✓ Check-ins1:05
Performing rotations (old) ✓ Check-ins1:17
Performing reflections: rectangle (old) ✓ Check-ins2:26
Performing reflections: line (old) ✓ Check-ins1:16
Determining translations (old) ✓ Check-ins0:46
Rotation examples (old) ✓ Check-ins2:27
Determining rotations (old) ✓ Check-ins1:59
Dilating lines ✓ Check-ins3:59
Unit 11: Congruence
Transformations and congruence
Triangle congruence
Theorems concerning triangle properties
Working with triangles
Theorems concerning quadrilateral properties
- Proof: Opposite sides of a parallelogram ✓ Check-ins8:30
- Proof: Diagonals of a parallelogram ✓ Check-ins9:06
- Proof: Opposite angles of a parallelogram ✓ Check-ins4:08
Proof: The diagonals of a kite are perpendicular ✓ Check-ins11:06- Proof: Rhombus diagonals are perpendicular bisectors ✓ Check-ins4:04
Proof: Rhombus area ✓ Check-ins5:07
Proofs of general theorems that use triangle congruence
Unit 12: Similarity
Definitions of similarity
Introduction to triangle similarity
Solving similar triangles
Angle bisector theorem
Solving problems with similar and congruent triangles
Solving modeling problems with similar and congruent triangles
Unit 13: Trigonometry
Special right triangles
Special right triangles intro (part 1) ✓ Check-ins ✎ Fixed a slip9:30
Special right triangles intro (part 2) ✓ Check-ins ✎ Fixed a slip9:39
30-60-90 triangle example problem ✓ Check-ins6:40
Special right triangles proof (part 1) ✓ Check-ins6:59
Special right triangles proof (part 2) ✓ Check-ins5:42
Area of a regular hexagon ✓ Check-ins7:51
Introduction to the trigonometric ratios
Solving for a side in a right triangle using the trigonometric ratios
Modeling with right triangles
Trigonometric ratios and similarity
Sine and cosine of complementary angles
The reciprocal trigonometric ratios
The law of sines
The law of cosines
Solving general triangles
Unit 14: Circles
Circle basics
Arc measure
Arc length (from degrees)
Introduction to radians
Arc length (from radians)
Inscribed shapes problem solving
Proof: Right triangles inscribed in circles ✓ Check-ins5:35
Inscribed shapes: find diameter ✓ Check-ins2:33
Inscribed shapes: angle subtended by diameter ✓ Check-ins5:49
Inscribed shapes: find inscribed angle ✓ Check-ins2:10
Inscribed quadrilaterals proof ✓ Check-ins3:56
Solving inscribed quadrilaterals ✓ Check-ins4:58
Properties of tangents
Proof: Radius is perpendicular to tangent line ✓ Check-ins8:41
Proof: Segments tangent to circle from outside point are congruent ✓ Check-ins3:56
Tangents of circles problem (example 1) ✓ Check-ins4:37
Tangents of circles problem (example 2) ✓ Check-ins3:47
Tangents of circles problem (example 3) ✓ Check-ins2:34
Area of inscribed triangle
Standard equation of a circle
Expanded equation of a circle
Unit 15: Analytic geometry
Distance and midpoints
Dividing line segments
Problem solving with distance on the coordinate plane
Parallel and perpendicular lines on the coordinate plane
Equations of parallel and perpendicular lines
Parallel lines from equation ✓ Check-ins3:48
Parallel lines from equation (example 2) ✓ Check-ins3:03
Parallel lines from equation (example 3) ✓ Check-ins2:42
Perpendicular lines from equation ✓ Check-ins3:29
Writing equations of perpendicular lines ✓ Check-ins3:01
Writing equations of perpendicular lines (example 2) ✓ Check-ins1:45
Proof: parallel lines have the same slope ✓ Check-ins5:49
Proof: perpendicular lines have opposite reciprocal slopes ✓ Check-ins8:55
Challenge: Distance between a point and a line
Unit 16: Geometric constructions
Constructing bisectors of lines and angles
Constructing regular polygons inscribed in circles
Constructing circumcircles and incircles
Constructing a line tangent to a circle
Unit 17: Miscellaneous
Worked examples
Challenge problems: perimeter & area ✓ Check-ins8:13
Challenging perimeter problem ✓ Check-ins9:56
CA Geometry: Deductive reasoning ✓ Check-ins10:17
CA Geometry: Proof by contradiction ✓ Check-ins ✎ Fixed a slip11:56
CA Geometry: More proofs ✓ Check-ins ✎ Fixed a slip12:12
CA Geometry: Similar triangles 1 ✓ Check-ins12:55
CA Geometry: More on congruent and similar triangles ✓ Check-ins ✎ Fixed a slip11:11
CA Geometry: Triangles and parallelograms ✓ Check-ins11:14
CA Geometry: Area, pythagorean theorem ✓ Check-ins10:19
CA Geometry: Area, circumference, volume ✓ Check-ins ✎ Fixed a slip10:53
CA Geometry: Pythagorean theorem, area ✓ Check-ins ✎ Fixed a slip10:44
CA Geometry: Exterior angles ✓ Check-ins ✎ Fixed a slip10:53
CA Geometry: Pythagorean theorem, compass constructions ✓ Check-ins12:35
CA Geometry: Compass construction ✓ Check-ins12:49
CA Geometry: Basic trigonometry ✓ Check-ins ✎ Fixed a slip11:04
CA Geometry: More trig ✓ Check-ins12:21
CA Geometry: Circle area chords tangent ✓ Check-ins10:06
Speed translation ✓ Check-ins ✎ Fixed a slip9:57
Learn this with a class
With a class on Puzzicle this course runs as a timetable of live study parties: your batch watches together and answers the check-ins, sometimes with a teacher leading.
Course content © Khan Academy, used under CC BY-NC-SA. See this course on Khan Academy.