LAW OF COSINE.
The Law of Cosine
a2 = b2 + c2 – 2bc cos(A)
b2 = a2 + c2 – 2ac cos(B)
c2 = a2 + b2 – 2ab cos(C)
The Cosine Rule can be used in any triangle where you are trying to relate all three sides to one angle.
if you need to find the length of a side, you need to know the other two sides and the opposite angle.
The Law of Cosine is useful when you know the to adjacent side and internal angle between that two side than Length of
third sidecan be find out by this equation .