prove that the length of a line segment drawn from the point P (x0 , y0) and perpendicular to the line g: y = mx+n ( m ≠ 0 ) is | mx0 - y0 + n | / root m^2 + 1
evidence g: y=mx+n (m ≠ 0 ) suppose the perpendicular from P cut g on Q. Equation of the line PQ is ?