Linear function
The parametric or vector or vector-parametric form has 1 parameter t, 2 variables x and у, and 4 constants a1, a2, x1, and y1. The coefficients a1, a2, x1, and y1 are not uniquely determined. The line passes through the points А=(x1,y1) and B=(x1+a1,y1+a2) so that taking taking any other points or even just reversing the order ot the points will result in different constants for the same line.