Geometry: Angles
35 video lessons available
Angle Basics
Definition of an angle. How to denote an angle using points on the angle (including the vertex)
Source: Salman Khan - Khan Academy
All Lessons in This Course
Angle Basics
Definition of an angle. How to denote an angle using points on the angle (including the vertex)
Introduction to angles (old)
What an angle is. Angles in a circle. Complementary and supplementary angles.
Measuring Angles in Degrees
How to measure an angle in degrees
Using a Protractor
Measuring Angles
Using the KA virtual protractor to measure angles
Angle-a-trons
This is a follow-up from Being a Plant part 2
Acute Right and Obtuse Angles
The difference between acute, obtuse and right angles
Acute Obtuse and Right Angles
Complementary and Supplementary Angles
Basics of complementary, supplementary, adjacent and straight angles. Also touching on what it means to be perpendicular
Identifying Complementary and Supplementary Angles
Angles (part 2)
More on complementary and supplementary angles. Introduction to opposite angles.
Proof - Sum of Measures of Angles in a Triangle are 180
Proof that the sum of the measures of the angles in a triangle are 180
Triangle Angle Example 1
Figuring out angles in a triangle. A little about exterior angles being the sum of the remote interior angles
Angles at the intersection of two lines
Figuring out angles at the intersection of two lines
Proof-Vertical Angles are Equal
Proving that vertical angles are equal
Angles (part 3)
Angles formed when a transversal intersects parallel lines
Angles formed between transversals and parallel lines
Angles of parallel lines
Proof - Corresponding Angle Equivalence Implies Parallel Lines
Proof by contradiction that corresponding angle equivalence implies parallel lines
Angles of parallel lines
The angles formed between parallel lines and a transversal
Angles of parallel lines 2
Angles of parallel lines examples
Triangle Angle Example 2
Another example finding angles in triangles
Triangle Angle Example 3
Multiple ways to solve for the angles of multiple triangles
Finding more angles
Finding more angles
The Angle Game
Using what we know to solve for angles in the Angle Game.
Angle Game (part 2)
More examples of the Angle Game.
More on why SSA is not a postulate
SSA special cases including RSH
Angles Formed by Parallel Lines and Transversals
Parallel lines, transversal lines, corresponding angles
Point Line Distance and Angle Bisectors
Thinking about the distance between a point and a line. Proof that a point on an angle bisector is equidistant to the sides of the angle and a point equidistant to the sides is on an angle bisector
Two column proof showing segments are perpendicular
Using triangle congruency postulates to show that two intersecting segments are perpendicular
Angle Bisector Theorem Examples
Using the angle bisector theorem to solve for sides of a triangle
Angle Bisector Theorem Proof
What the angle bisector theorem is and its proof
Inscribed and Central Angles
Showing that an inscribed angle is half of a central angle that subtends the same arc
Perpendicular Radius Bisects Chord
Simple proof using RSH postulate to show that a radius perpendicular to a chord bisects it
Inradius Perimeter and Area
Showing that area is equal to inradius times semiperimeter
2003 AIME II Problem 7
Area of rhombus from circumradii of triangles
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35 lessons in this course