Please help with maths question?

Question

a man owns a wolf, a donkey and a cabbage and needs to transport his possessions across a river in a rowing boat, which is only large enough to hold himself and one of his possessions(the cabbage is very large) the cabbage cannot be left alone with the donkey, otherwise it would be eaten. For the same reason, the donkey cannot be left with the wolf. how can he get all his belongings safely across the river?

Answer 1

Given three variables x, y and z satisfying the following equality
x + y + z = 9{x^(2\3)+y^(2\3)+z^(2\3)}
and x; y; z are R+, prove that
summation{(xy\x+y+2z)}>=.25