Tue Quadratic Equation

Suppose that we substitute the graph B in the triple (A,B,C) by the graph D :

Then we need to prove that   P(B) * P(D) = P(A)^2 + P(C)^2

But by simple algebra we can simplify this expression to:
                     
                                                                M(B) * M(D) = M(A)^2 * z^(nb/2 + 2) * y^(wb) * x^(hb) + M(C)^2