# triangles   83 videos

• #### 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
• #### Area and Perimeter of Triangles

##### Pre-AlgebraIntroductory Geometry

Understanding why the area of a triangle is 1/2 base times height

• #### Similar Triangles

##### Pre-AlgebraIntroductory Geometry

Overview of similarity: congruent angles, proportional corresponding sides

• #### HL

##### GeometryTriangles

How to use the hypotenuse leg shortcut to determine the congruence of right triangles.

hypotenuse leg triangle congruence right triangles
• #### Proportional Segments Between Parallel Lines

##### GeometrySimilarity

How to prove two triangles are similar using a line parallel to a base.

parallel lines triangles similar triangles proportion
• #### Indirect Measurement

##### GeometrySimilarity

How to use similar triangles to measure the height of objects.

indirect measurement similar triangles measurement
• #### Converse of the Pythagorean Theorem

##### GeometryPythagorean Theorem

How to use the converse of the Pythagorean Theorem to determine if a triangle is a right triangle, how to use Pythagorean triples to memorize the lengths of certain right triangles.

right triangle leg hypotenuse converse Pythagorean triples
• #### Converse of the Pythagorean Theorem

##### TrigonometryPythagorean Theorem

How to use the converse of the Pythagorean Theorem to determine if a triangle is a right triangle, how to use Pythagorean triples to memorize the lengths of certain right triangles.

right triangle leg hypotenuse converse Pythagorean triples
• #### Similarity Shortcuts

##### GeometrySimilarity

How to determine if two triangles are similar using a shortcut.

similar triangles AA SAS SSS proportion congruence
• #### CPCTC

##### GeometryTriangles

How to use the principle that corresponding parts of congruent triangles are congruent, or CPCTC.

corresponding parts or congruent triangles proofs
• #### Inverse Trigonometric Functions

##### GeometryBasic Trigonometry

How to use inverse trig functions to find angles in right triangles.

trigonometry right triangle inverse sine cosine tangent
• #### Inverse Trigonometric Functions

##### TrigonometryBasic Trigonometry

How to use inverse trig functions to find angles in right triangles.

trigonometry right triangle inverse sine cosine tangent
• #### Inverse Trigonometric Functions

##### PrecalculusBasic Trigonometry

How to use inverse trig functions to find angles in right triangles.

trigonometry right triangle inverse sine cosine tangent
• #### Constructing Altitudes

##### GeometryConstructions

How to define an altitude and draw them on acute, right, and obtuse triangles.

altitudes perpendicular segment vertex opposite side obtuse acute right triangles
• #### SSS and SAS

##### GeometryTriangles

How to use the SAS and SSS shortcuts to determine the congruence of two triangles.

triangle congruence side side side side angle side
• #### ASA and AAS

##### GeometryTriangles

How to use the ASA and AAS shortcuts to determine the congruence of two triangles.

triangle congruence angle side angle angle angle side
• #### Trigonometric Ratios: Sine

##### GeometryBasic Trigonometry

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

trigonometry ratio right triangle sine SOH CAH TOA
• #### 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
• #### Trigonometric Ratios: Tangent

##### GeometryBasic Trigonometry

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

trigonometry ratio right triangle sine SOH CAH TOA
• #### Trigonometric Ratios: Sine

##### TrigonometryBasic Trigonometry

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

trigonometry ratio right triangle sine SOH CAH TOA