Question

http://www.saylor.org/site/wp-content/uploads/2011/06/MA-2.5.pdf page:13 (where it says :",where N is either |L-1| or |L+1| depending on whether L is positive or negative why |L-1|?

Answer 1

well N depicts a value and |L-1|=|L+1| if left L is negative and right L is positive;)

Answer 2

Suppose L is -8, then L+1=-7 and L-1=-9
That makes f(x) between -9 and -7.
|f(x)| will be between 7 and 9, so less than 9.
That means that in that case |f(x)| is less than |L-1|.