Two equations "combined" don't give the desired result

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    Special relativity
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Homework Help Overview

The discussion revolves around the application of the Lorentz transformation equations in the context of relativity. The original poster expresses confusion regarding the combination of two specific equations from a physics text, particularly focusing on how to derive a relation between time coordinates.

Discussion Character

  • Exploratory, Mathematical reasoning, Assumption checking

Approaches and Questions Raised

  • The original poster attempts to combine equations from the text but encounters difficulties in simplifying the results. They question whether their algebraic manipulation is correct or if additional equations are needed for the derivation.

Discussion Status

Some participants have provided feedback on the original poster's attempts, indicating that the simplification may indeed be valid with minor adjustments. The original poster acknowledges this feedback and expresses intent to revisit their calculations.

Contextual Notes

The original poster notes a potential typo in the equations presented in the text, which may affect their understanding of the derivation process. They are specifically interested in the author's method rather than alternative derivations.

nomadreid
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Homework Statement
From only (A) x'=g(x-vt) and (B) x^2-(ct)^2=x'^2-(ct')^2 derive
(C) t'=g(t-(vx/c^2)),
Relevant Equations
g= gamma = 1/sqrt(1-(v/c)^2) and the equations in the Statement
In https://phys.libretexts.org/Bookshe...__Relativity/5.06:_The_Lorentz_Transformation

First, the equation (5.6.7) apparently has a typo: the x' should not be in the denominator, as one can see by comparing it with the equation just above it from which it was derived. The corrected equation is Equation (A) in the Statement (standard Lorentz transformation).

Then two equations down (unnumbered), the author states the equation (B) in the Statement,
"We combine this with Equation 5.6.7 that relates x and x' to obtain the relation between t and t′:"
and then states the equation (C) in the statement.

How he means to "combine" them is what I don't successfully get. I tried substitution of x' from (A) into (B), and got a mess; I then tried solving (B) for x', and substituting this solution into (A), and got the same mess, that is,
(A) into (B)

first mess.PNG

which doesn't simplify to (C). Either: (a) my algebraic manipulation is wrong; (b) the author is including some other equation in the derivation.
Any indications where this is going wrong would be greatly appreciated. (Yes, there are other ways to derive the relation (C), but I am interested in this author's derivation.)
 
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nomadreid said:
which doesn't simplify to (C)
Yes it does (up to the sign of the square root).
 
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Thanks, Orodruin. OK, I will try again, now with the assurance that I just made some minor mistake made in simplifying. That fully answers my question! Super!
 
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update: found the error. It all comes out. Thanks again, Orodruin
 

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