Answer: The formula for the area of a circle.
Explanation:
1. The formula for calculate the area of a circle is:

Where r is the radius of the circle.
2. By definition, the number π is an irrational number, because it cannot be expressed as a simple fraction. Therefore, if you want to calculate the area of a circle, the result will be an irrational number.
3. Then, the answer is the first option.