Corbett Maths
Cyclic Quadrilateral – Proof
What do you call a quadrilateral in danger? A peril-lelogram! Scholars avoid danger by proving the opposite angles in a quadrilateral add up to 180 degrees. After viewing a brief video, they complete textbook exercises and a practice...
Corbett Maths
Angle in a Semi-Circle – Proof
Young mathematicians observe a geometric proof using a short video. They see each part of the diagram clearly labeled and the simple math written off to the side. The new knowledge helps them solve additional problems independently.
CK-12 Foundation
Arcs in Circles: Lesson
Taking a major look at arcs is not minor. A segment of an extensive playlist on geometry introduces the concept of an arc in a circle. The resource demonstrates how to find the measure of an arc and defines special types of arcs.
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: Three Points Defining a Circle
Demonstates that any three non-collinear points can be used to define a unique triangle with a unique circumcenter and circumradius. These, in turn, define a unique circle. The center of the circle is the circumcenter of the triangle....
Khan Academy
Khan Academy: Algebra: Conic Sections: Three Points Defining a Circle
A video lesson that describes how any three non-collinear points actually define a circle. First it is shown that three points define a triangle. Then it is shown that the circumcenter of that triangle is actually the center of the...
Khan Academy
Khan Academy: Geometry: Area of Inscribed Equilateral Triangle (Basic Trig Used)
Demonstrates how to find the area of an equilateral triangle inscribed in a circle by applying the area formula for a circle and Heron's formula. Some basic trigonometry (SOHCAHTOA) is also used. [11:38]
Khan Academy
Khan Academy: Geometry: Language and Notation of the Circle
Formally defines a circle and different parts of a circle. Identifies the proper notation for naming different parts of a circle. [11:12]
Virtual Nerd
Virtual Nerd: Construct Equilateral Triangle and Square Inscribed in a Circle
Two videos on geometric constructions. One explains how to construct an equilateral triangle using a ruler and compass. The second describes how to draw a square using a compass and a straightedge.
Khan Academy
Khan Academy: Triangles: Right Triangles Inscribed in Circles (Proof)
This video tutorial 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.
Imagine Learning Classroom
Learn Zillion: Lesson Video: 'Show Angle Relationships in Cyclic Quadrilaterals'
In this lesson, you will show angle relationships in cyclic quadrilaterals by using the Central Angle Theorem. [3:27]
Khan Academy
Khan Academy: Perpendicular Bisectors: Area Circumradius Formula Proof
Proof of the formula relating the area of a triangle to its circumradius.
Khan Academy
Khan Academy: Triangles: Circumcenter of a Triangle
Multiple proofs showing that a point is on a perpendicular bisector of a segment if and only if it is equidistant from the endpoints. Using this to establish the circumcenter, circumradius, and circumcircle for a triangle.
Khan Academy
Khan Academy: Triangles: Area of Inscribed Equilateral Triangle
Students explore a problem that requires then to figure out the area of an equilateral triangle inscribed in a circle using a little trigonometry.
Khan Academy
Khan Academy: Introduction to Euclidean Geometry: Language of the Circle
In this video student learn formal definition of a circle including tangent and secant lines, diameters, radii, major and minor arcs.
Khan Academy
Khan Academy: Circles: Inscribed and Central Angles
Showing that an inscribed angle is half of a central angle that subtends the same arc.
Study Pug
Study Pug: Angles in a Circle
Video shows how to find an angle inscribed in a circle. [1:58]
Khan Academy
Khan Academy: Area of Inscribed Equilateral Triangle
A worked example of finding the area of an equilateral triangle inscribed within a circle who's area is known. This video uses Heron's formula and some trigonometry.
Khan Academy
Khan Academy: Geometric Constructions: Circle Inscribed Square
Sal constructs a square that is inscribed inside a given circle using compass and straightedge.
Khan Academy
Khan Academy: Geometric Constructions: Circle Inscribed Regular Hexagon
Sal constructs a regular hexagon that is inscribed inside a given circle using compass and straightedge.
Khan Academy
Khan Academy: Geometric Constructions: Triangle Inscribing Circle
Sal constructs a circle that inscribes a given triangle using compass and straightedge.
Khan Academy
Khan Academy: Geometric Constructions: Triangle Circumscribing Circle
Sal constructs a circle that circumscribes a given triangle using compass and straightedge.
Khan Academy
Khan Academy: Inscribed Shapes: Angle Subtended by Diameter
One method using an inscribed angle intercepting a diameter of a circle.
Khan Academy
Khan Academy: Proof: Right Triangles Inscribed in Circles
Proof showing that a triangle inscribed in a circle having a diameter as one side is a right triangle.