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I'd take the difference, then normalise it relatively and take the absolute value.

As for the other one, you probably want to look at projecting a point from an origin location, a certain distance at a certain angle. If you look in the source of Raiko (or pretty much any other open source bot) you'll see the 'project' function. Once you have the new location of the point, you can calculate the distance the normal way, sqrt((x1-x2)^2 + (y1 - y2)^2).