Learn Geometry
The whole high school geometry course, worked on the figure itself. Tap the angles and sides, name the rule that connects them, and the board checks that it really holds.
417 lessons417 challenges610 quiz questions
- Beginner friendly
Hands-on interactive lessons
Audio narration on every lesson
Quizzes to test your knowledge
Free certificate of completion
Syllabus
Section 1
Angles
Start sectionStartAngles from the ground up, worked on the figure itself: naming and measuring them, the pairs a straight line and a full turn make, vertical angles, parallel lines cut by a transversal, and the angle facts every triangle obeys. Every step names its reason.Meet the Angle
4 lessons4Naming and Equations
3 lessons3Right Angles and Complements
6 lessons65Vertical Angles
5 lessons55Around a Point
5 lessons510The Angle Bisector
4 lessons410Parallels and Transversals
6 lessons6Angle Chases
5 lessons55Triangle Angle Sum
5 lessons520Isosceles and Equilateral
6 lessons615The Exterior Angle
5 lessons55Final Challenges
5 lessons510Section 2
Triangles
Start sectionStartTriangles by their sides, worked on the figure: sorting them, when three lengths can meet, perimeter and area, the Pythagorean theorem and the special right triangles, then similar triangles and the proportions that scale them.The Triangle Inequality
4 lessons4Sides and Names
4 lessons4Perimeter
5 lessons520Area of a Triangle
6 lessons610The Pythagorean Theorem
5 lessons515Finding a Leg
5 lessons520Is It Right?
5 lessons515Special Right Triangles
6 lessons615Similar Triangles
5 lessons515Scale in the World
5 lessons55Two Tools at Once
5 lessons510Final Challenges
5 lessons515Section 3
Congruence & Proof
Start sectionStartProving things about figures: statements and reasons, congruent triangles by SSS, SAS, ASA, AAS and HL, what congruence gives you, and proofs with vertical angles, parallel lines, isosceles triangles and similar triangles.What a Proof Is
4 lessons4Congruent Triangles
3 lessons3SSS
5 lessons5SAS
6 lessons65ASA and AAS
5 lessons55HL for Right Triangles
5 lessons5Using CPCTC
5 lessons5Proofs with Vertical Angles
5 lessons5Proofs with Parallel Lines
5 lessons5Isosceles Triangle Proofs
6 lessons610Similarity Proofs
6 lessons65Final Challenges
5 lessons5Section 4
Polygons & Quadrilaterals
Start sectionStartPolygons and their angle sums, regular polygons, exterior angles, parallelograms, rectangles, rhombi, squares, trapezoids and kites, drawing on squared paper, and the areas of quadrilaterals and composite shapes.Polygons
5 lessons5Regular Polygons
3 lessons3Exterior Angles
5 lessons515Parallelograms
6 lessons610Rectangles, Rhombi, Squares
5 lessons510Trapezoids and Kites
5 lessons55On Squared Paper
5 lessons510Area of Parallelograms
5 lessons515Area of Trapezoids
5 lessons55Composite Shapes
5 lessons510Polygon Chases
5 lessons510Final Challenges
5 lessons55Section 5
Circles
Start sectionStartCircles on the figure: radii and diameters, circumference and area in exact terms of pi, arcs and sectors, inscribed angles, angles in a semicircle and on the same arc, cyclic quadrilaterals, and tangents.Parts of a Circle
3 lessons3Circumference
4 lessons4Area of a Circle
5 lessons520Arcs and Sectors
5 lessons520Radii Make Isosceles
5 lessons515Inscribed Angles
6 lessons615Angles in a Semicircle
5 lessons515Angles on the Same Arc
5 lessons510Cyclic Quadrilaterals
5 lessons510Tangents
6 lessons615Circle Chases
5 lessons55Final Challenges
5 lessons520Section 6
Transformations & Constructions
Start sectionStartMoving shapes exactly: translations, reflections, rotations, dilations and symmetry on a grid, drawing on squared paper, then compass and straightedge constructions that still work when the figure moves.Translations
4 lessons4Reflections
5 lessons5Rotations
5 lessons510Combining Moves
5 lessons510Dilations
5 lessons510Symmetry
5 lessons55Drawing on Squared Paper
6 lessons625Compass and Straightedge
5 lessons5Bisectors
5 lessons5Perpendiculars and Parallels
5 lessons5Constructed Shapes
5 lessons5Final Challenges
5 lessons510Section 7
Surface Area & Volume
Start sectionStartSolids and their measures: prisms, cylinders, pyramids, cones and spheres, their volumes and surface areas in exact terms of pi, slant heights by Pythagoras, and working backwards from a measure to a missing length.Volume of Prisms
6 lessons6Solids and Their Parts
3 lessons3Cylinders
5 lessons510Pyramids
5 lessons55Cones
5 lessons5Spheres and Hemispheres
5 lessons5Surface Area of Prisms
6 lessons6Surface Area of Cylinders
5 lessons55Pyramids and Cones Outside
5 lessons5Spheres Outside
5 lessons515Mixed Solids
5 lessons510Final Challenges
5 lessons55
Learn by Solving
Work every problem yourself on an interactive board. Each step is a move you choose, every line is checked, and graphs are drawn by hand.
Solving is a game of legal moves. You pick the move; every line follows from the one before it.
Build Your Math Streak
Stay consistent and watch your progress grow! Track your daily math habit, protect your streak with freeze days, and earn rewards for showing up every day.
12 days streak
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Double or Nothing
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You're Not Alone
Compete on global leaderboards, invite friends to earn rewards, and celebrate each other's wins. Math is better with friends!
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Promotion zoneEvery way to learn
Read, listen, test yourself, ask the AI about your own steps, or look up anything you've already covered. Every lesson meets you where you are.
An equation is a claim: the two sides name the same number. The equals sign asserts sameness, it gives no orders.
A solution is a value of the unknown that makes the claim true. Substitute it and both sides agree.
Solving means changing the form without changing the claim: the same move applied to both sides keeps the balance.
Earn a Certificate
Earn a certificate when you complete a section. Add it to your LinkedIn profile to show how far your math has come.
Certificate of Completion
Math Fundamentals
Add to LinkedInWhy learn geometry with Coddy
- You do the geometry, not only the algebra. Each step starts with the reason: vertical angles, the angle sum of a triangle, the Pythagorean theorem. The board checks that the rule holds in that figure.
- More than finding x. Drag a point and watch a theorem hold, draw on squared paper, build constructions with a compass and straightedge, move shapes with transformations, and write two-column proofs.
- Exact answers. Lengths stay as radicals like 2√13 and circle measures stay in π, so you see the real answer, not a rounded one.
- Free certificate of completion you can share on LinkedIn or your resume. It's proof you finished an interactive Geometry course, not just watched videos.
Frequently asked questions about learning geometry
What does the geometry course cover?
Seven sections: angles and parallel lines, triangles and the Pythagorean theorem, congruence and proof, polygons and quadrilaterals, circles, transformations and constructions, and surface area and volume.
How do you solve a geometry problem on Coddy?
Tap the angle or side you want, pick the rule that gives it from a menu, and its value appears on the figure. When a label holds a letter, the board writes the rule's equation and you solve it.
Does the course teach geometry proofs?
Yes. You build two-column proofs line by line, with statements taken from the figure and reasons such as SSS, SAS, ASA, AAS, HL and CPCTC. Each line is checked, and SSA is refused with the reason it fails.
Do I need algebra before geometry?
Only linear equations, such as 2x + 10 = 90. Coddy's Algebra course teaches them from zero.
Is the geometry course free?
Yes, every lesson and problem is free. Pro removes the daily limit and adds unlimited help from the AI tutor.
Do I get a Geometry certificate when I finish?
Yes. When you complete the Geometry course you receive a free certificate of completion that you can share on LinkedIn or add to your resume.
