If an object is under effect of 2 forces where there is an alpha angle between them;

If the angle is a good one like 60, 90 or 120; and

$latex F_1 = F_2 = F$ then;

$latex for \alpha = 60\textdegree; R=\sqrt{3}F;$

$latex for \alpha = 90\textdegree; R=\sqrt{2}F;$

$latex for \alpha = 120\textdegree; R=F;$

Shortcut: If three forces are acting on same object

If three forces are acting on the same object like shown on the picture and if they are in balance;

Then the force opposite to the biggest angle will have the smallest value, the force opposite to the biggest value will have the biggest value.