The Law of Sines (or Sine Rule) is very useful for solving triangles:


a
sin A
=
b
sin B
=
c
sin C

It works for any triangle:

a, b and c are sides.

A, B and C are angles.

(Side a faces angle A,
side b
faces angle B and
side c faces angle C).

And it says that:

When we divide side a by the sine of angle A
it is equal to side b divided by the sine of angle B,
and also equal to side c divided by the sine of angle C

Sure … ?

Well, let’s do the calculations for a triangle I prepared earlier:

5,8,9 Triangle


a
sin A
=
8
sin(62.2°)
=
8
0.885…
= 9.04…


b
sin B
=
5
sin(33.5°)
=
5
0.552…
= 9.06…


c
sin C
=
9
sin(84.3°)
=
9
0.995…
= 9.04…

The