2.2.74 Derivatives and Differentials

Condition: let \ (\ quad u = \ frac {1} {x} (\ varphi (x-y)+\ psi (x+y)) \), where \ (\ varphi \) and \ (\ psi \)-differentiated functions. Show that \ [\ frac {\ partial} {\ partial x} \ left (x^} \ frac {\ partial u} {\ partial x} \ right) = x^{2} \ frac {\ partial^{2}^{2}^{2}^{2} u} {\ partial y^{2}} \]