Limits, flipping approaching direction

[plutonium]

I recently found the proof that lim x-> 0 sinx/x = 1
http://www.geocities.com/pkving4math2tor4/4_the_elem_transc_func/4_01_01_03_lim_of_trig_func.htm

There is this one step I don't get.
http://www.geocities.com/pkving4mat..._01_01_03_lim_of_trig_func_files/image020.gif

How did they flip the direction that x approaches from?

 

[courtrigrad]

They let $$t = -x$$