Question

Express each of the types of Riemann sums that follow in general sigma notation and also as an expanded sum. You may assume that f is a function defined on $[a,b],$n is a positive integer, $∆x=\frac{b-a}{n},\mathrm{and}{\mathrm{k}}_{\mathrm{x}}=\mathrm{a}+\mathrm{k}∆\mathrm{x}.$

right sum.

Short answer

The general sigma notation of the right sum and its expanded sum is following.
$\sum _{k=1}^{n}f\left(x_k\right)∆x=\sum _{k=1}^{n}f\left[a+k\left(\frac{b-a}{n}\right)\right]\left(\frac{b-a}{n}\right)$

Step-by-step solution

Step 1. Given information.

The given type of Riemann sum is the right sum.

Step 2. the right sum. 

Consider the function defined on the interval $\left[a,b\right]$and n is a positive integer.

Then The n-rectangle right sum for f on $\left[a,b\right]$is $\sum _{k=1}^{n}f\left({\stackrel{}{x}}_k\right)∆x.$

Where $∆\mathrm{x}=\frac{\mathrm{b}-\mathrm{a}}{2},{\stackrel{*}{\mathrm{x}}}_{\mathrm{k}}=\mathrm{a}+\mathrm{k}∆\mathrm{x},\&{\stackrel{*}{\mathrm{x}}}_{\mathrm{k}}\in [x_{\mathrm{k}-1},x_{\mathrm{k}}]$

then expanded sum will be the following

$$\begin{gathered} \sum _{k=1}^{n}f\left(x_k\right)∆x=\sum _{k=1}^{n}f(a+k∆x)∆x \\ \sum _{k=1}^{n}f\left(x_k\right)∆x=\sum _{k=1}^{n}f\left[a+k\left(\frac{b-a}{n}\right)\right]\left(\frac{b-a}{n}\right) \end{gathered}$$