# the cosine double angle formulas   65 videos

• #### The Law of Cosines

##### GeometryBasic Trigonometry

How to define and use the law of cosines.

law of cosines ratios triangles
• #### Angle of Elevation and Depression

##### GeometryBasic Trigonometry

How to define an angle of elevation or an angle of depression.

trigonometry angle of elevation angle of depression
• #### Supplementary and Complementary Angles

##### GeometryGeometry Building Blocks

How to identify supplementary and complementary angles.

angles sum right angle
• #### Inscribed Angles

##### GeometryCircles

How to calculate the measure of an inscribed angle.

inscribed angle intercepted arc central angle congruent arcs
• #### Polygon Angle Sum

##### GeometryPolygons

How to derive the formula to find the sum of angles in any polygon.

triangle angle sum diagonal polygon
• #### Remote Interior Angles

##### GeometryTriangles

How to define exterior angles and their remote interior angles and how to prove their properties.

exterior angle remote interior angle non adjacent angle
• #### Corresponding Angles

##### GeometryReasoning, Diagonals, Angles and Parallel Lines

How to define corresponding angles and their special properties.

parallel lines angles congruence
• #### Angle Bisectors

##### GeometryGeometry Building Blocks

How to label an angle bisector; how to use an angle bisector to find a missing variable.

congruent angles ray
• #### Duplicating an Angle

##### GeometryConstructions

How to duplicate an angle using a compass and straightedge.

congruent angles construction compass straightedge
• #### Trigonometric Ratios: Cosine

##### GeometryBasic Trigonometry

How to define the cosine ratio and identify the cosine of an angle in a right triangle.

trigonometry ratio right triangle sine SOH CAH TOA
• #### Solving Formulas

##### GeometryArea

How to strategize about solving formulas for variables; how to solve the area of a rectangle formula for base and height; how to solve the area of a triangle formula for base and for height.

formulas isolating a variable rectangle area triangle area trapezoid area regular polygon area
• #### Exterior Angles of a Polygon

##### GeometryPolygons

How to find the sum of the exterior angles in a polygon and find the measure of one exterior angle in an equiangular polygon.

exterior angle sum of angles equiangular polygon
• #### Angles in Semicircles and Chords to Tangents

##### GeometryCircles

How to prove that an angle inscribed in a semicircle is a right angle; how to solve for arcs and angles formed by a chord drawn to a point of tangency.

inscribed angle semicircle tangent chord intercepted arc
• #### Alternate Interior Angles

##### GeometryReasoning, Diagonals, Angles and Parallel Lines

How to define alternate interior angles and their special properties.

parallel lines angles congruence interior transversal
• #### Alternate Exterior Angles

##### GeometryReasoning, Diagonals, Angles and Parallel Lines

How to define alternate exterior angles and their special properties.

parallel lines angles congruence exterior transversal
• #### Triangle Angle Sum

##### GeometryTriangles

How to apply the triangle angle sum theorem.

triangle angle sum theorem 180 degrees
• #### Angles: Types and Labeling

##### GeometryGeometry Building Blocks

How to label an angle and how to differentiate between acute, right, obtuse, and straight angles.

angle acute right obtuse straight vertex side

##### GeometryReasoning, Diagonals, Angles and Parallel Lines

vertex side coplanar
• #### Triangle Side and Angle Inequalities

##### GeometryTriangles

How to determine the relationship between the side inequalities and angle inequalities in a triangle.

angles smallest to largest sides smallest to largest
• #### Vertical Angles

##### GeometryReasoning, Diagonals, Angles and Parallel Lines

How to define and identify vertical angles.

vertex intersecting lines congruent