# Spacetime diagram [closed]

I need your help. I've just begun learning about space time diagrams. Below is my doubt:

An event is shown as a point on a spacetime diagram. Another frame has coordinates of space and time as:

\begin{aligned} c t^{\prime} &=(\cosh \theta)(c t)-(\sinh \theta) x \\ x^{\prime} &=(-\sinh \theta)(c t)+(\cosh \theta) x \\ y^{\prime} &=y \\ z^{\prime} &=z \end{aligned} It's said that the new spacetime diagram could be drawn on the previous spacetime diagram as shown below: Then is that the time coordinate of the event in the new frame can be found as shown below (red line is parallel to the $$x'$$ line, $$(a, b)$$ is the intersection point of red line with $$ct'$$ axis) Hence the new time coordinate is $$c t^{\prime}=\sqrt{a^2+b^2}$$ ? Is that correct?

• Not it is wrong, you can not use Pythagoras in this diagram. imagine a=1 what would b be since the x' system moves with v. Sep 23 at 13:07
• Related : Your identical closed post here Angle in a spacetime diagram. Sep 24 at 2:53