In VBA (Visual Basic for Applications), you can utilize math functions by calling them directly in your code. VBA has a wide array of built-in math functions that you can use to perform calculations, such as trigonometric functions, logarithms, and rounding functions, among others.
Here’s how you can use some of the common math functions in VBA:
1.

**Abs**: Returns the absolute value of a number.```
Dim result As Double
result = Abs(-3.14) ' result is 3.14
```

2. **Sqr**: Returns the square root of a number.```
Dim result As Double
result = Sqr(4) ' result is 2
```

3. **Sin**,**Cos**,**Tan**: Return the trigonometric sine, cosine, and tangent of an angle, respectively (angle must be in radians).```
Dim angleRadians As Double
Dim sinValue As Double
angleRadians = PI / 4 ' PI / 4 radians is 45 degrees
sinValue = Sin(angleRadians) ' sin(45 degrees)
```

4. **Atn**: Returns the arctangent of a number (result is in radians).```
Dim x As Double
Dim result As Double
x = 1
result = Atn(x) ' result is the arctangent of x
```

5. **Exp**: Returns the exponential of a number (e raised to the power of a number).```
Dim result As Double
result = Exp(1) ' result is e^1 which is approximately 2.71828
```

6. **Log**: Returns the natural logarithm (base e) of a number.```
Dim result As Double
result = Log(10) ' result is natural log of 10
```

7. **Rnd**: Returns a random number between 0 and 1.```
Dim result As Double
result = Rnd() ' result is a random value between 0 and 1
```

8. **Round**: Rounds a number to a specified number of decimal places.```
Dim result As Double
result = Round(3.14159, 2) ' result is 3.14
```

9. **Int**and**Fix**: Return the integer portion of a number.```
Dim result As Double
result = Int(3.99) ' result is 3
```

To use these functions in a VBA module, you simply call them just as in the examples above. Here is a sample subroutine that demonstrates how to use some math functions:
```
Sub UseMathFunctions()
Dim radius As Double
radius = 5
' Calculate the circumference of a circle
Dim circumference As Double
circumference = 2 * PI * radius ' Using Pi as a constant for simplicity
' Calculate a random number
Dim randomNumber As Double
randomNumber = Rnd() ' Will give you a random decimal value from 0 to 1
' Use the round function to round the circumference to 2 decimal places
circumference = Round(circumference, 2)
' Output the results in a message box
MsgBox "The circumference of the circle with radius " & radius & " is " & circumference
MsgBox "A random number is " & randomNumber
End Sub
```

Remember to declare any variables you use and to use the correct data types for your calculations. Some functions may require you to include a specific library, but for the most part, these functions are built into VBA and do not require additional libraries.