I understand the strategy. The textbook gives 2 hints. It says to use theorem 3.1.2 and to use the solution of the previous problem. Unfortunately, I have not been able to find the solution of previous problem. I posted the previous problem at
http://www.mathhelpforum.com/math-he...ntegrable.html
but no one gave any idea. If I get an idea out of the previous problem, I can solve this problem because it appears to be related.
Partition of [a, b] will be (b-a) / n where n is the number of increments. So the partition will look like
{a, a + (b-a)/n , a + (b-a)/n + (b-a)/n, ......b}