Find the area under the curve using Archimedes's method for 2x+1 from zero to some number b.

So we divide the area under the parabolic segment into rectangles. Where we divide the segment b into n parts where we have (b/n) sections and k=1,2,3,...,n.

So the area of the rectangles are:

.....but the answer should be +b not +b/n. Any help is appreciated. Thank you!