In a rhombus, each side has length $6.$ One of the angles of the rhombus is $120^\circ.$ Find the area of the rhombus.
Well draw a rhombus.
Draw the diagonals.
See how it forms four 30, 60, 90 triangles?
I will leave the rest up to you.
Do it yourself. Ya know how equilateral triagles work? Do that.
Clearly comes from AOPS, probably.