A Treatise on Differential Equations
Andrew Russell Forsyth
Andrew Russell Forsyth ... For we then have X (r, 6, c) = 0 as the equation of the family of curves. ... we have d6 tan b = r dr while, if P be the same quantity for the trajectory, and R and 6) be the polar coordinates of a point on it, d(8) tan q2 = R ...