Law of Cosine

Do you know!!!

Formula for Law of Cosine

c^2 = a^2 + b^2 - 2ab cos(C)

b^2 = a^2 + c^2 - 2ac cos(B)

a^2 + b^2 + c^2 - 2bc cos(A)



When do you use this?

You use the Law of Cosine for finding a missing side for a triangle, or a missing angle.

Examplessssssssssssssssss!!

In the triangle ABC, side b = 12, side c = 20, and m < A = 40 degrees. Find side A to the nearest interger.

a^2 = 12^2 + 20^2 - 2(12)(20)(cos 40)

a^2 = 144 + 400 - 480(.7660)

a^2 = 176.2988

a = 13.2777 about 13