i must admit i did it a different way. i used m and n to get a pair of simultaneous expressions (m, n >0, m - n =/= 0), then did x0/y0 in terms of x1, x2, y1, y2. i then cross multiplied and collected like m and n's, so that m(x0y2-x2y0) = n(x0y1-x1y0).
i then multiplied both sides by...