Could someone please explain to me what’s wrong here?

$ \cfrac{x}{4} = \cfrac{y}{x} = \cfrac{7}{y}$

So $ $ \cfrac{x^2}{4} = y \ \ \ \ \ \ \ \text{and} \ \ \ \ \ \ \ y = \sqrt{7x}$ $

Hence $ $ \cfrac{x^2}{4} =\sqrt{7x}$ $

With a solution of $ x = 2.57$

But $ $ \cfrac{2.57^2}{4} \neq \sqrt{7 (2.57)}$ $