Paper 3, Section I, G

Geometry
Part IB, 2018

Consider a quadrilateral ABCDA B C D in the hyperbolic plane whose sides are hyperbolic line segments. Suppose angles ABC,BCDA B C, B C D and CDAC D A are right-angles. Prove that ADA D is longer than BCB C.

[You may use without proof the distance formula in the upper-half-plane model

ρ(z1,z2)=2tanh1z1z2z1zˉ2]\left.\rho\left(z_{1}, z_{2}\right)=2 \tanh ^{-1}\left|\frac{z_{1}-z_{2}}{z_{1}-\bar{z}_{2}}\right| \cdot\right]