Have you heard of Riemann Sums?

Results 1 to 6 of 6

- Aug 28th 2009, 04:35 PM #1

- Joined
- Aug 2009
- Posts
- 11

## What Do These Question Mean?

Through these problems, express the given limit as a definite integral over the indicated interval [a,b]. Assuming that [xi-1,x] denotes the ith subinterval of a subdivision of [a,b] into n subintervals, all with the same length Δx = (b-a/n, and that mi =1/2(xi-1 + xi is the midpoint of the ith subinterval.

qqqqqqqqqqn

qqqlimqqqqqΣ (x^3-3xi^2 +1) Δx over [0,3]

qqqqn->∞qi=1

qqqqqqqqqqn

qqqlimqqqqqΣ (25-xi^2)^0.5 Δx over [0,5]

qqqn->∞qqi=1

Please show work and explain, I am very lost . Ignore the q's in the formulas.

- Aug 28th 2009, 04:38 PM #2

- Joined
- Jan 2009
- Posts
- 290

- Aug 28th 2009, 04:45 PM #3

- Joined
- Aug 2009
- Posts
- 66

- Aug 28th 2009, 05:10 PM #4
Use Latex please: http://www.mathhelpforum.com/math-he...-tutorial.html

I see a lot of q's and n's too

- Aug 28th 2009, 05:15 PM #5

- Joined
- Apr 2005
- Posts
- 18,207
- Thanks
- 2428

That's because most browsers do not respect "spaces" at beginnings of lines. In order to maintain the spacing, he put "q" at the beginnings of lines. Any way, LaTex is better. They are:

over [0, 3]

and

over [0, 5]

Billy Maize, obviously whoever gave you these problems expects you to know about the "Riemann sums" chengbin refers too. You can hardly expect a tutorial here but the basic idea is to divide the x-axis into a number of intervals, use the height of the function at each point to construct rectangles, then add the areas of the rectangle to approximate the integral.

Taking the limit, as the number of intervals goes to infinity and goes to 0, gives the exact integral. What you want to write for your answer is something like . Now what do you think a, b, and f(x) is for each of those? (I'll give you this hint- becomes dx!)

- Aug 29th 2009, 08:35 AM #6