Directions: Using the digits 1 to 9 as many times as you want, fill in the boxes to make the biggest circle:
Where is it better to put the larger values?
To make the circle bigger, the radius needs to be as large as possible. So, putting a 9 there makes it the biggest. The coefficients of x and y need to be as small as possible so they both need to be 1.
Source: Robert Kaplinsky