Understanding geometry problem in relativity

[Vrbic]

Homework Statement

It is not ordinary problem, it is connected to it. I don't understand a figure and how is described. The problem is here http://www.pmaweb.caltech.edu/Courses/ph136/yr2011/1102.2.K.pdf How did equation 2.4 from figure 2.3 arise? Why disappear $\Delta t^2$ from the right?
Another question is: In the text above eq.2.4 is written $c\Delta t^2=\Delta t^2$?? Ok, if it says work in geometric units where $c=1$ ok, but it isn't mentioned.

Homework Equations

eq 2.4 $\Delta s^2=-\Delta t^2+\Delta x^2+\Delta y^2=-(2h-\Delta y^2)+\Delta y^2$

The Attempt at a Solution

An attempt occurred in my mind, when I thought about it half an hour :-)

Thank you all.

 

[jedishrfu]

So you figured it out?

 

[Vrbic]

So you figured it out?

No, second equality in 2.4 is out of me. $-\Delta t^2+\Delta x^2+\Delta y^2=-(2h-\Delta y)^2 + \Delta y^2$