Law of Sines: a/sin A = b/sin B = 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.
Related Law of Sines identities
Common questions
What is the Law of Sines identity?
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.
When do you use the Law of Sines identity?
SSA is the ambiguous case - it can yield two triangles, one, or none, so always check whether a second angle also fits.
Which identities are related to Law of Sines?
Law of Sines belongs to the Law of Sines group. The identities used alongside it most often are 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.
Or browse all 45 identities in the full reference, or read the trigonometry guides for the method behind them.