Let us multiply the LHS of Eqn 5 by the LHS of 6 and equate the
result to the product of the RHS’s to get
xx
! = γ2
(xx
! + xut! − x
!
ut − u2
tt!
), and upon setting x = ct, x! = ct! we get(8)
c2
tt! = γ2
(c2
tt! + uctt! − uct!
t − u2
tt!
) and now upon cancelling tt! (9)
γ2 = 1
1 − u2
c2
(10)
γ = 1
!
1 − u2
c2
. (11)
Note that once we have found γ it does not matter that we got
it form this specific event involving a light pulse. It can applied to
Eqns. (5,6) valid for a generic event. Putting γ back into Eqn. (6)
we obtain
x
! = x − ut
!
1 − u2
c2
. (12)
If we now go to Eqn 5 and isolate t
! we find