Problem 4 Let x,yx,yx,y be two positive real numbers such that x4−y4=x−yx^4-y^4=x-yx4−y4=x−y . Prove that x−yx6−y6≤43(x+y).\frac{x-y}{x^6-y^6}\leq \frac{4}{3}(x+y).x6−y6x−y≤34(x+y).