Find the center of gravity of a homogeneous tetrahedron, without knowledge of the integral calculus, and with little knowledge of physics this problem is not easy at all: it was a serious scientific problem in the days of Archimedes or Galileo. Thus, if we wish to solve it with as little preliminary knowledge as possible we should look around for a simpler analogous the Corresponding problem in the plane occurs here naturally:
Find the center of gravity of a homogeneous triangle.