\fLet z1 = x1 + iy1 and z2 = X2 + iy2 be two points in H with y1 = y2. Derive a formula for the hyperbolic distance dHz (21, Z2). Hint: horizontal translations are hyperbolic isometries. Use z z tv where v has zero imaginary part so that |Re(z1 + v) | = |Re(z2 + v)|