Real numbers $x$ and $y$ have an arithmetic mean of 18 and a geometric mean of $\sqrt{92}$. Find $x^2+y^2$.
I recognize that the arithmetic mean of $x$ and $y$ is the average of $x$ and $y$, so I can write $\frac{x+y}{2}=18$. I also recognize that the geometric mean of $x$ and $y$ is the square root of the product of $x$ and $y$, so I can write $\sqrt{xy}=\sqrt{92}$. I want to find $x^2+y^2$, so I wonder if I can use these two equations to eliminate one of the variables and get a quadratic equation in the other. If I square both sides of the first equation, I get $\frac{(x+y)^2}{4}=324$, which expands to $x^2+2xy+y^2=1296$. If I square both sides of the second equation, I get $xy=92$. I can use this to substitute for $xy$ in the first equation, and get $x^2+2(92)+y^2=1296$, which simplifies to $x^2+y^2=1112$.

