Finding the maximum of function f (x) = - X-2 / X

Finding the maximum of function f (x) = - X-2 / X

Derivation = - 1 + 2 / x ^ 2
Let the derivative be zero, x = √ 2 or - √ 2
X < - √ 2, derivative greater than 0, function increasing, x = - √ 2 is the maximum point
f(x)max=f(-√2)=2√2