Define Lami's theorem.

Explanation

The magnitude of each force of the system is proportional to sine of the angle between the other two forces. The costant of propotionality is same for all three forces.
`|vecF_(1)|propto sin alpha`
`|vecF_(2)| propto sin beta`
`|vecF_(3)| propto sin gamma`
Therefore, `(|vecF_(1)|)/(sin alpha)= (|vecF_(2)|)/(sin beta)= (|vecF_(1)|)/(sin gamma)`.