Paper 3, Section I, F

Geometry
Part IB, 2010

(i) Write down the Poincaré metric on the unit disc model DD of the hyperbolic plane. Compute the hyperbolic distance ρ\rho from (0,0)(0,0) to (r,0)(r, 0), with 0<r<10<r<1.

(ii) Given a point PP in DD and a hyperbolic line LL in DD with PP not on LL, describe how the minimum distance from PP to LL is calculated. Justify your answer.