Path Integral Doubt: How Did Shankar Deduce S/h>pi?

[sumeetkd]

I just read the chapter in Shankar regarding path integrals (the 8th)
I didnt quite get how he deduced that destructive interference in the summation
sets in after S/h>pi.(This is the first section itself)
I couldn't find reference to such a thing elsewhere.

 

[weejee]

I hope this will help.

http://en.wikipedia.org/wiki/Stationary_phase_approximation