# Understanding geometry problem in relativity

#### Vrbic

1. The problem statement, all variables and given/known data
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.

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

3. The attempt at a solution
An attempt occurred in my mind, when I thought about it half an hour :-)

Thank you all.

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#### jedishrfu

Mentor
So you figured it out?

#### Vrbic

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

"Understanding geometry problem in relativity"

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