# Upper and Lower Riemann Sums

• November 6th 2007, 08:14 PM
taypez
Upper and Lower Riemann Sums
Compute the upper and lower Riemann sums and the integral from zero to 1 of f(x)dx, where the partition is

P= {0, 2/5, 1/2, 3/5, 1}

Thanks.
• November 6th 2007, 09:11 PM
ThePerfectHacker
Quote:

Originally Posted by taypez
Compute the upper and lower Riemann sums and the integral from zero to 1 of f(x)dx, where the partition is

P= {0, 2/5, 1/2, 3/5, 1}

Thanks.

What is f(x)?
• November 7th 2007, 05:34 AM
taypez
f(x) = 1-x^2
• November 7th 2007, 06:52 AM
kalagota
Quote:

Originally Posted by taypez
Compute the upper and lower Riemann sums and the integral from zero to 1 of f(x)dx, where the partition is

P= {0, 2/5, 1/2, 3/5, 1}

Thanks.

$f(x) = 1 - x^2$

f(x) is decreasing from 0 to 1. hence, for the given partition:

$U(P,f) = 1\cdot \frac{2}{5} + \frac{21}{25} \cdot \frac{1}{10} + \frac{3}{4} \cdot \frac{1}{10} + \frac{16}{25} \cdot \frac{2}{5} = \frac{163}{200}$

$L(P,f) = \frac{21}{25} \cdot \frac{2}{5} + \frac{3}{4} \cdot \frac{1}{10} + \frac{16}{25} \cdot \frac{1}{10} + 0 \cdot \frac{2}{5} = \frac{19}{40}$
• November 7th 2007, 10:42 AM
taypez
Can you give me an example of a couple calculations on how you arrived at these numbers for U(f,P)? I came up with some different ones and I can't find my mistake.

Thanks.
• November 7th 2007, 10:44 AM
ThePerfectHacker
Quote:

Originally Posted by taypez
Can you give me an example of a couple calculations on how you arrived at these numbers for U(f,P)? I came up with some different ones and I can't find my mistake.

Thanks.

Because U(f,P) is calculated by taking the supremum (largest value) on each interval. So since the function was decreasing the largest value is the left-endpoint.