How do you convert from v=i+j form to ax+by=c form?

So that's vector notation. In vector notation we use i, j, k. They have hats on them as well. i will correspond to the x axis and j will correspond to the y axis and k to the z axis if you're working with 3-d models. a and b are just scalars that are being multiplied to the vectors. Just substitute i = ax and j = by and v = c