Thanks, invariance of space-time interval gives alternative way for me to prove my case.
$$(c \Delta t')^2 - (\Delta x')^2 = (c \Delta t)^2 - (\Delta x)^2$$
Assume $$x'=-x$$ then
$$\Delta x' = x/\gamma - x'$$
$$\Delta x = x - x'/\gamma$$
Since $$x'=-x$$ then
$$\Delta x' = x/\gamma - (-x)$$
$$\Delta x = x - (-x/\gamma)$$
So
$$\Delta x = \Delta x'$$
So, based on the invariance of the space-time interval
$$(c \Delta t')^2 = (c \Delta t)^2$$
You have to do better than the above. Saying 1=1 or two events are infact the same event measured in proper time is not an argument for anything.