where the eqn of the original line is ax+by+c=0

Is it acceptable to treat the line as the point P(a,b) to ultimately find point R (the end location of P) and ignore the point c (simply adding it back in at the end of the work) I ask this as my lecturer told us all we should follow 5 steps.

1. Move the point Q to the origin so we can use the rotation matrix and hence subtract Q from P which we will call P'.

2. Then turn the point P' into a column matrix.

3.Multiply by the rotational matrix

4. Turn the new column vector into a coordinate R'

5. Turn R' into R (our desired point) by adding Q to R'

I am extremely confused as to what to do once we have ascertained this point R, as I end up with no points without a coefficient of x or y when I convert R into an eqn with the coordinates as coefficients of x and y in an eqn of form ?x+?y=0 I know the answer has similar points as simply constants.

So is my understanding of the principles ok or am I misinterpreting something along the way.

Thanks in advance