Law of Sines: a/sin A = b/sin B = c/sin C

\dfrac{a}{\sin A} = \dfrac{b}{\sin B} = \dfrac{c}{\sin C}

In any triangle, each side divided by the sine of its opposite angle gives the same value: a/sin A = b/sin B = c/sin C. Use it for AAS, ASA, and SSA. SSA is the ambiguous case - it can yield two triangles, one, or none, so always check whether a second angle also fits.

oblique

Related Law of Sines identities

Circumradius form

Practise it

Reading a formula is not the same as recalling it under time pressure. The workspace drills Law of Sines questions in the quiz, and the triangle solver shows a worked solution for any triangle you type in.

Practise Law of Sines Open the triangle solver

Or browse all 45 identities in the full reference, or read the trigonometry guides for the method behind them.