Riemann Sum Calculator

To calculate the left or right Riemann sum, select the type, enter the function, fill the required input fields, and click calculate button using the Riemann sum calculator

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Riemann Sum Calculator

Approximate the definite integral of any function using the Riemann Sum calculator. It can find the Riemann sum of both types. The prominent feature of this tool is its detailed results covering all the necessary steps of computation.

How to use this tool?

To use the Riemann sum calculator, you will have to:

  1. Enter the function with the help of the keyboard.
  2. Select the variable.
  3. Enter the upper and lower limits along with the subinterval.
  4. Choose the sum type.
  5. Click Calculate.

What is the Riemann Sum?

Riemann sums are a bridge between discrete mathematics (where we add up the areas of individual rectangles) and continuous mathematics (where we find the exact area under a curve using integration). 


It is the foundation of integral calculus and provides a method for approximating and understanding areas under curves, which is a problem with countless applications in science, engineering, statistics, and economics.


Imagine you have a graph with a curve on it, and you want to find the area between the curve and the x-axis over a certain interval. This is not always straightforward, especially if the curve is irregular and doesn't form simple geometric shapes like rectangles or triangles, whose areas we can easily calculate.


Integration is a fundamental concept in calculus that allows us to find the area under curves. When a function is integrated, we are essentially adding up an infinite number of infinitesimally thin rectangles under the curve. The exact area under the curve from point a to b is given by the definite integral of the function.


Since we can't actually sum up an infinite number of rectangles (because we can't deal with infinitely small things in a practical calculation), the Riemann sum is used to approximate the area under the curve by summing up a finite number of rectangles. The more rectangles one uses, the closer one gets to the exact area.


The formula of Riemann Sum:

The Riemann sum can be written as a summation:

\[\sum_{i=1}^{n} f(x_i^*) \Delta x\]

As the number of subintervals increases (and thus Δx decreases), the approximation becomes more accurate.  In the limit, as the width of the subintervals approaches zero Δx→0 the Riemann sum converges to the exact value of the definite integral, which is denoted by:

\[\int_{a}^{b} f(x) \, dx\]

Types of Riemann Sum:

The types of Riemann sums generally refer to how the heights of the rectangles are determined for the approximation of the area under a curve. When we partition the interval [a,b] into smaller subintervals, the choice of where the function is evaluated to get the height of each rectangle leads to different types of Riemann sums. 

Left Riemann Sum: 

For the left Riemann sum, the height of each rectangle comes from the function value at the left endpoint of each subinterval. 

If you have partitioned your interval into n subintervals, then for the ith subinterval, you would use f(a + (i - 1)Δx) as the height of the rectangle, where Δx is the width of each subinterval. 

Right Riemann Sum:

The right Riemann sum uses the function value at the right endpoint of each subinterval. So, the height of each rectangle for the ith subinterval is determined by f(a + iΔx)

How to calculate the Riemann Sum:

Let's break this down step by step:

Choose an Interval: You decide on the section of the curve you're interested in, from point a to point b on the x-axis.

Divide the Interval: You split this interval into smaller sections (subintervals). This is like slicing up the space under the curve into vertical strips.

Draw Rectangles: For each subinterval, you draw a rectangle. The width of each rectangle is the width of the subinterval, and the value of the function determines the height at a certain point within the subinterval. This point could be the left end, the right end, or the middle of the subinterval, depending on the type of Riemann sum you're using.

Calculate Areas: Each rectangle's area is easy to calculate: width × height. The width is the subinterval's length, and the height is the function's value at your chosen point within the subinterval.

Add Up Areas: You add the areas of all these rectangles together. This sum is the Riemann sum and gives you an approximation of the area under the curve.

Refining the Approximation: If you want a better approximation, you use more rectangles. The thinner the rectangles (which means the more of them you have), the less empty space there is between the curve and the tops of the rectangles, and the better they will approximate the area under the curve.


Compute a Riemann sum for the function f(x) = x2 on the interval [0, 2] using 4 equal subintervals with the Left Riemann Sum approach. This means, using the left endpoint of each subinterval to determine the height of each rectangle.


Step 1: Determine Δx.

The interval [0, 2] is divided into 4 subintervals, so 

Δx = [(b - a)/n]

Δx = [2 - 0/4] = 0.5

Step 2: Identify the x-values for the left Rieman sum.

For the Left Riemann Sum, the x-values are the left endpoints of each subinterval: 0, 0.5, 1, and 1.5.

Step 3: Evaluate the function at these x-values.

We evaluate f(x) at each of these points:

f(0) = 02 = 0

f(0.5) = (0.5)2 = 0.25

f(1) = 12 = 1

f(1.5) = (1.5)2 = 2.25

Step 4: Calculate the left Riemann sum.

L = f(0)Δx + f(0.5)Δx + f(1)Δx + f(1.5)Δx

Plugging in the values:

L = (0 * 0.5) + (0.25 * 0.5) + (1 * 0.5) + (2.25 * 0.5)

L = 0 + 0.125 + 0.5 + 1.125

L = 1.75

Applications of Riemann sum:

Riemann sums are a fundamental concept in calculus, and they have a variety of applications across different fields of science, engineering, economics, and beyond. Here are some key applications:

Physics: In physics, Riemann sums are used for computing work done by a variable force, the center of mass of an irregular object, electric charge distribution, and other quantities that require integration.

Engineering: In engineering fields, Riemann sums help in the design and analysis of systems, such as determining the area for heat transfer, analyzing signal processing, and calculating the materials needed for construction.

Probability & Statistics: In probability theory, Riemann sums are used to approximate the areas under probability density functions to find probabilities of different outcomes.

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