Law of Sines

Law of cosines is not applicable when two angles and one side (AAS or ASA) or one angle and two sides (angle not included (SSA)) of an oblique triangle are given. In order to handle such situation, we use another law known as "law of sines".

Statement:

If a,b,c are three sides and α,β,γ are three angles of an oblique triangle with usual notation, then law of sines is stated as follows:

Proof:

Consider an obtuse triangle ABC as shown in the figure below. Let h be the height of triangle ABC with respect to base AC. In right Δ ABD,