Khan Academy

Proof: Radius is perpendicular to tangent line

Proof: Segments tangent to circle from outside point are congruent

Tangents of circles problem (example 1)

Tangents of circles problem (example 2)

Tangents of circles problem (example 3)

Geometric constructions: circle tangent

Geometric constructions: circle tangent (example 2)

Angles, arc lengths, and trig functions — Basic example (K-A)

Angles, arc lengths, and trig functions — Harder example (K-A)

Arc length from subtended angle (K-A)

Subtended angle from arc length (K-A)

Finding arc measures (K-A)

Finding arc measures with equations (K-A)

Intro to arc measure (K-A)

Circles glossary (K-A)

Proof: all circles are similar (K-A)

Radius, diameter, circumference and π (K-A)

Area of a shaded region (K-A)

Area of inscribed equilateral triangle (K-A)

Finding circumference of a circle when given the area (K-A)

Area of a sector (K-A)

Partial circle area and arc length (K-A)

Area of combination of solids (K-A)

Problem types: surface area of combination of solids (K-A)

Problem types: volume of combination of solids (K-A)