The game: get the green function f(x) to pass through the blue points ) and .
To reset, click the top-right corner.
The function f is controlled by m and b, or rise, run, and b at left. To get more precise values, type them into the input bar at the bottom. For example, you might have to type "m=8/3".
The points can be moved by clicking and dragging. They will snap to integer values if close enough. Or, in the input bar, you can type in A=(x, y) for whatever values you like.
There are various checkboxes that show or hide information. Have fun! Send me feedback!

Keep somewhere on the y-axis to start, and experiment by moving the other point around.
Can you predict when m must be negative?
What if the points are horizontal? Vertical?