The question and solution for this problem are in problem #5 from the attached pdf. What I don't get at all are the M and |s1|, |s2|, |s3|, ... , |sn0| parts at the end. Also, is the inequality with the equal sign combined technically equal in this case? As for the triangle inequality itself, does the less than part only or usually apply for the magnitudes of vectors or something?

Any help would be greatly appreciated!

Thanks in advance!