The midpoint of the line segment between $(x,y)$ and $(2,4)$ is $(-7,0)$. Find $(x,y)$.
I know that the midpoint of a line segment is the average of the endpoints' coordinates. That means I can set up a system of equations where the midpoint's $x$-coordinate is the average of the endpoints' $x$-coordinates, and the same for the $y$-coordinates. So I have $\frac{x+2}{2}=-7$ and $\frac{y+4}{2}=0$. I can simplify these equations by multiplying both sides by $2$, so I get $x+2=-14$ and $y+4=0$. Solving for $x$ and $y$, I get $x=-16$ and $y=-4$. Therefore, the other endpoint of the line segment is $(-16,-4)$. 