precalc
posted by Anonymous .
According to an article by Thomas H. McMahon in the July 1975 issue of Scientific American, a treeâ€™s height varies directly with the radius of the base of its trunk. He expressed this relation using the formula h = kr^2/3 where k is a constant, h is the treeâ€™s height, and r is the treeâ€™s radius.
Now suppose you own a stand of trees whose pulp can be used for making paper. The amount of wood pulp you can produce from a tree increases as the treeâ€™s volume increases. The model approximates a tree without its branches as a right circular cone. The formula for the volume of the tree then becomes V = (1/3)Ï€r^2h.
Substituting the formula for height of a tree in the formula for volume of a tree, the new formula for volume becomes

taking your formulas at face value and guessing that
the strange symbol is supposed to be π,
sub h = kr^2/3 into V = (1/3)πr^2h
to get
V = (1/3)πr^2(kr^2/3)
= (1/9)kr^4