I am reading Richard A. Brualdi 's book Introductory Combinatorics (5th Edition).
In p.273, the author introduced the correspondence between the multiplication schemes for the n numbers a1, a2, ... and triangularizations of convex polygonal regions of n + 1 sides.
It is very intuitive.
However, how does the multiplication schemes (or triangularizations) corresponds to the -1s 1s sequences in p.266.
Is there any intuitive way to turn the -1s 1s sequences problem to the multiplication schemes (or triangularizations)?
Very thanks.