Corbett Maths
Radius and Tangent – Proof
A tangent line always finds its place at a 90-degree angle to a radius. Many scholars struggle with the proof of the seemingly simple statement. A brief video demonstrates the reasoning behind the proof before pupils practice applying it...
CK-12 Foundation
Inscribed Angles in Circles: Lesson
Circle the angles and intercept the arcs. The video introduces three theorems relating to inscribed angles in circles. Using drawings, the segment of a playlist on geometry illustrates the measure of angle along with theorems about two...
CK-12 Foundation
Chords in Circles: Lesson
Strike a chord with four theorems. The segment of a playlist on geometry introduces four basic theorems about chords in a circle. Theorems include the relationships between diameters and chords, congruent chords and arcs, and congruent...
CK-12 Foundation
Angles Outside a Circle: Lesson
Understand the difference in finding angle measures. A segment of an extensive geometry playlist introduces the formula to find the measure of an angle formed outside of a circle. Using examples, the video shows how to calculate measures...
CK-12 Foundation
Inscribed Quadrilaterals in Circles: Lesson
Find supplementary information about inscribed angles. A section of a large geometry playlist introduces the relationship of angles in an inscribed quadrilateral. The presentation works through examples that use the relationship between...
Khan Academy
Khan Academy: Geometry: Right Triangles Inscribed in Circles (Proof)
This video tutorial [5:35] explains that if the diameter of a circle is one of the sides of a triangle inscribed in the circle then the triangle is a right triangle. This video also appears in the strand Geometry: Circles.
Khan Academy
Khan Academy: Geometry: Inscribed and Central Angles
Proof that the measure of an inscribed angle is half the measure of a central angle when the angles intercept the same arc. [14:16]
Khan Academy
Khan Academy: Proof: All Circles Are Similar
Demonstrates how to use a unit circle on a coordinate grid to prove that all circles are similar. [1:34]
Khan Academy
Khan Academy: Geometry: Inradius Perimeter and Area
Proof that the area of a triangle is equal to half the inradius times the perimeter of the triangle, or the area is equal to the inradius times the semiperimeter. This video also appears in the Geometry: Circles strand. [7:29]
Khan Academy
Khan Academy: Perpendicular Radius Bisects Chord
Proof that if a radius is perpendicular to a chord then it bisects the chord. This video also appears in the Geometry: Circles strand. [6:57]