4.5. Law of Cosines http://www.ck12.org
4.5 Law of Cosines
Here you will solve non-right triangles with the Law of Cosines.
The Law of Cosines is a generalized Pythagorean Theorem that allows you to solve for the missing sides and angles
of a triangle even if it is not a right triangle. Suppose you have a triangle with sides 11, 12 and 13. What is the
measure of the angle opposite the 11?
Watch This
MEDIA
Click image to the left for use the URL below.
URL: http://www.ck12.org/flx/render/embeddedobject/58142http://www.youtube.com/watch?v=pGaDcOMdw48 Khan Academy: Law of Cosines
Guidance
The Law of Cosines is:
c^2 =a^2 +b^2 − 2 ab·cosC
It is important to understand the proof:
You know four facts from the picture: