I understand this: 23 mod 4

 - it gives me the remainder on dividing 23 by 4

But how can I do the same thing with, say, 23.4 and 5.2?

The reason I ask is because I want to divide angles (float values) by (2*Pi) (another float) and just get the remainder, i.e. I want to discard multiples of (2*Pi) from my angle.

I want to plot a bunch of straight lines with positive slope in one colour, and I want to plot a single line of negative slope in another colour.

I hope my code is self-explanatory:

restart; with (plots):
myEqns:=NULL:
for i from 1 to 5 do;
 myEqns:=myEqns,y-x=i;
od:
myEqns:=[myEqns];
 [y - x = 1, y - x = 2, y - x = 3, y - x = 4, y - x = 5]
implicitplot([op(myEqns), y+x=0], x=-10..10, y=-10..10, colour=[red,blue]);