Remember how we needed to have a right triangle to use SohCahToa? Well, that's no longer true. As long as your triangle is not a donkey in disguise, you can use the Laws of Sines and Cosines to solve any triangle. This lesson focuses on the Law of Cosines and does the impossible by generalizing the Pythagorean Theorem for all triangles.

Deriving the Law of Cosines, Part 1

Duration_4_17

Deriving the Law of Cosines, Part 2

Duration_4_37

The Law of Cosines and Examples 2 and 3

Duration_4_30

Examples 1 (Revisited) and 4

Duration_4_37

Example 4 (Continued)

Duration_3_56

Example 5a

Duration_4_27

Example 5b

Duration_3_38

Geometry 7(B) apply the Angle-Angle criterion to verify similar triangles and apply the proportionality of the corresponding sides to solve problems.

Geometry 9(A) determine the lengths of sides and measures of angles in a right triangle by applying the trigonometric ratios sine, cosine, and tangent to solve problems

Geometry 9(B) apply the relationships in special right triangles 30º-60º-90º and 45º-45º-90º and the Pythagorean theorem, including Pythagorean triples, to solve problems