Find the minimum value of n

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Find the minimum $natural$ value of $n$ for given expression $$(x+y) ^2=nxy$$ I know that intuitively that the value will be minimum at x=y, but i want the mathematical logic behind it. Please don't send by doing it by $$A.M.>=G.M.$$ because I already know that method. Thanks.

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Note that $\frac{d}{dx}(x+y)^2/xy = [(xy)(2x+2y)-y(x+y)^2]/(xy)^2$ this is zero whenever $x=y$.

This is symmetric so it is the same story with the $y$ derivative. The value of the function at $x=y$ is $4$.

We can see this is a local minimum if we plot the graph. It is also clear that for the $(x,y)$ where this function is strictly positive, this is the minimum value the function takes.