12. (Hyperbolic angle measure) Consider the upper-half plane model for the hyperbolic plane H, where the set of points is H:= {(x, y) = R|y>0} and the set of lines is LH:= {ler | cr ER and r>0}U{le | CER}, non-vertical lines. vertical lines where ler = {(x, y) = H | (x-c) + y2 = r} and f = {(cy) Hy>0}. Elcrc, c mis a line Find the critical number ro = || r(P, ) for the line and the external point P, where l = lo, lo = {(x, y) = H | x=0}, and P = (1, 1). Use the following steps: (a) Suppose m is the line containing P such that ml. Show m = lo.v. (b) Show that m and intersect at the point (0, 2), call this point D.