Question answered here:
Area of triangle within a triangle
You really shouldn't double post, as this can cause the contributors here to unnecessarily duplicate effort.
Given a triangle ABC. On the sides: Let R lie one third of the way from A to B. Let S lie one third of the way from B to C. Let T lie one third of the way from C to A. Now connect points RST to make a triangle RST within triangle ABC. Prove that the area of triangle RST is equal to one third the area of triangle ABC.
Any help please?? I've tried law of sines and such to no avail.