There is no built-in function in Excel for computing proper or improper integrals. However, we can use a dedicated add-in, **ExceLab 365 Calculus Functions**, from the **Microsoft AppSource**. The add-in provides a function named **QUADF** that can calculate the integrals. But unfortunately, the QUADF function doesn’t always work as expected.

In this article, we’ll discuss why the **QUADF **function may be returning errors, and present an alternative way to calculate the integrals in Excel if and when it does.

## Reasons Why the QUADF Function Is Not Working in Excel and the Solution

There may be some issues with this add-in **QUADF** function. Sometimes it shows an error when it shouldn’t.

### Possible Reasons Why QUADF Is Not Working in Excel

The possible reasons why the function may not be working are:

- The
**QUADF**function is disabled in Excel. Install the**ExceLab 365 Calculus Functions Add-in**in your Excel application and it should then work. - If you fail to define an initial value in he function, it will return a
**#NUM! Error**. - But sometimes you get a
**#VALUE! Error**, which can be for several reasons, one of which is that the function is buggy in Excel 365.

To explain the problem, we have taken the following integral function to apply the **QUADF **function:

`∫(x²+2x+3)dx`

In this function, we set the lower limit **1** and the upper limit **4**.

To calculate the integral, we need to calculate the function value with a random **x1** value. For our case, we use **1** for the **x1** value, and we get the function value **6 **for that value.

At this point, we use the **QUADF** function for computing the integrals. In cell **C6** we enter the below formula:

`=QUADF(C5,X1,1,4)`

Here, **C5** is the function value** f**, and **X1** is the value for which we have the function value. **1** is the lower limit and **4** is the upper limit.

Press **ENTER**.

Oops! A **#VALUE! Error **is returned by the **QUADF** function.

#### A Suitable Solution Using the Mid Point Rule

From the above example, it is clear that the **QUADF** function is not working properly. Here is an alternative but effective solution to calculate the integrals, using the **MidPoint Rule**, also known as **Simpson’s Rule**. Conveniently, no add-ins are required to apply this method.

The value of the integral is **45** when we estimate it manually. Now, let’s try to show the same integral value using our method.

- In cell
**C17**, enter the following formula:

`=(4-1)/10`

Here, **4** and **1** represent the **b** and **a** values respectively, which are the **upper bound** and the **lower bound** of the integral. **10** is the number of steps (the **n Value**).

- Enter the formula given below in cell
**C18**:

`=C17/2`

Here, cell **C17** represents the value of **dx**.

- Insert the following formula in cell
**C5**:

`=1+C18`

Here, cell **C18** indicates the value of **dx/2**.

- In cell
**C6**, insert the following formula:

`=C5+$C$17`

As a result, wel have the **x Value** for the **2nd **step.

- Press
**ENTER**and drag down the**Fill Handle**tool to get the values for the other cells.

We have the following output for the **x Value**:

Now we will calculate the **f(x)** value.

- In cell
**D5**, enter the following formula:

`=C5^2+2*C5+3`

Here, cell **C5** refers to the **x Value**.

- Drag the formula down for the other cells to get the below output:

Now, we will calculate the individual integral values for each step.

- In cell
**E5**, enter the following formula:

`=D5*$C$17`

Here, cell **D5** indicates the **f(x) Value**.

Press **ENTER** and drag the formula down to get the result below:

Lastly, we use the **SUM function** to evaluate the sum of the integral values.

- In cell
**E15**, insert the following formula:

`=SUM(E5:E14)`

This will calculate the arithmetic sum of all **10** integral values.

- Press
**ENTER**and drag the formula down to other cells.

The **Final Integral Value** of **44.9775** is so close to our desired result of **45**.

So, we can say that the **Mid Point Rule** is an effective workaround to the issue of *QUADF **not working*.

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