Algebra for Geometry: Free Course

About this course

Geometric relationships provide a setting for algebraic reasoning. This course uses triangle angles, similarity and the Pythagorean theorem to find unknown measurements. Study the complete public source playlist from Khan Academy in English, with all 13 recordings in the on-site classroom. Original lesson titles, source order and repeated entries are preserved.

Course at a glance

What you’ll learn

• Use triangle angle sums to solve for unknown angles.
• Identify and justify triangle similarity.
• Write proportions using corresponding sides.
• Apply the Pythagorean theorem to right-triangle lengths.

Skills you’ll gain

• Triangle angles
• Similarity
• Proportional reasoning
• Pythagorean theorem

Course Overview

Angle-sum examples connect a geometric fact with an equation. Similar-triangle lessons require matching corresponding sides and angles before writing proportions; one example deliberately uses the same segment in different roles. The Pythagorean recordings then relate the sides of a right triangle and provide repeated worked practice. These are complementary tools with different hypotheses. A visually similar sketch is not enough to justify a similarity statement, and the Pythagorean theorem requires a right triangle. Label the correspondence and the right angle explicitly before deciding which relationship fits the problem.

How to study the course

• Videos 1–3: this part of the source list includes “Proof: Sum of measures of angles in a triangle are 180” through “Similar triangle basics”. Label what is given before applying a property. Keep a brief working note, revisit an unclear explanation and test one example before moving to another part of the material.
• Videos 4–6: this part of the source list includes “The Pythagorean theorem intro” through “Similar triangle example problems”. Separate an observation in a drawing from a justified conclusion. Keep a brief working note, revisit an unclear explanation and test one example before moving to another part of the material.
• Videos 7–9: this part of the source list includes “Pythagorean theorem 2” through “Pythagorean theorem 3”. Redraw an example with different dimensions or orientation. Keep a brief working note, revisit an unclear explanation and test one example before moving to another part of the material.
• Videos 10–13: this part of the source list includes “Similarity example where same side plays different roles” through “Triangle angle example 3”. Explain the relationship that supports the answer. Keep a brief working note, revisit an unclear explanation and test one example before moving to another part of the material.

Who is this for?

This course suits learners studying geometry and teachers looking for recorded explanations of the named geometric topic. It also provides a recorded reference for revisiting a topic after an earlier lesson or study attempt. Choose examples appropriate to your background and allow time to work through the method instead of judging understanding only by how familiar the terminology sounds.

Before you start

Basic arithmetic and the algebra used in the examples are useful. Keep paper, a ruler and a compass when constructions are demonstrated.

Put the lessons into practice

Draw two similar triangles in different orientations and mark their corresponding vertices. Use a side ratio to find a missing length, explaining the correspondence. Solve a separate right-triangle problem and distinguish its theorem from the similarity argument. Check whether each answer is plausible relative to the other sides or angles.

This optional study activity is provided by WikiFree for independent practice. Keep your working notes and use the relevant classroom recording to check a step, definition or interpretation. It is not an instructor-marked assignment.

Certificate / Assessment

Watching the public videos and using WikiFree completion tracking does not award a certificate, academic credit, an examination voucher or instructor assessment. Use your practice output to review what you can explain and repeat independently. The recorded lessons provide study material; completion tracking records your progress through that material.

Frequently asked questions

Provider: Khan Academy. Videos play from the Khan Academy channel on YouTube.