Minimum Value Optimization 1
Let $ x $ and $ y $ be positive real numbers. Find the minimum value of
\[\left( x + \frac{1}{y} \right) \left( x + \frac{1}{y} + 2018 \right) + \left( y + \frac{1}{x} \right) \left( y + \frac{1}{x} + 2018 \right).\]
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Solution
By QM-AM,
\[\sqrt{\frac{(x + \frac{1}{y})^2 + (y + \frac{1}{x})^2}{2}} \ge \frac{(x + \frac{1}{y}) + (y + \frac{1}{x})}{2},\]so
\[\left( x + \frac{1}{y} \right)^2 + \left( y + \frac{1}{x} \right)^2 \ge \frac{1}{2} \left( x + \frac{1}{y} + y + \frac{1}{x} \right)^2.\]Then
\begin{align*}
&\left( x + \frac{1}{y} \right) \left( x + \frac{1}{y} + 2018 \right) + \left( y + \frac{1}{x} \right) \left( y + \frac{1}{x} + 2018 \right) \\
&= \left( x + \frac{1}{y} \right)^2 + \left( y + \frac{1}{x} \right)^2 + 2018 \left( x + \frac{1}{y} \right) + 2018 \left( y + \frac{1}{x} \right) \\
&\ge \frac{1}{2} \left( x + \frac{1}{y} + y + \frac{1}{x} \right)^2 + 2018 \left( x + \frac{1}{y} + y + \frac{1}{x} \right) \\
&= \frac{1}{2} u^2 + 2018u,
\end{align*}where $ u = x + \frac{1}{y} + y + \frac{1}{x} $.
By AM-GM,
\[u = x + \frac{1}{x} + y + \frac{1}{y} \ge 2 + 2 = 4.\]The function $ \frac{1}{2} u^2 + 2018u $ is increasing for $ u \ge 4, $ so
\[\frac{1}{2}u^2 + 2018u \ge \frac{1}{2} \cdot 4^2 + 2018 \cdot 4 = 8080.\]Equality occurs when $ x = y = 1, $ so the minimum value is $ \boxed{8080} $.
Freeflows