Final answer:
The area of a circle with a diameter of 18mm in terms of pi is 81π mm². This is derived using the formula A = πr² and taking half of the diameter as the radius (9mm).
Step-by-step explanation:
The area of a circle with a diameter of 18mm in terms of pi can be found using the area formula A = πr², where r is the radius of the circle. Since the diameter is 18 mm, the radius (r) is half of that which is 9 mm. Substituting r into the formula, we get
A = π(9 mm)²
which simplifies to
A = 81π mm²
This represents the area in terms of pi since we are not calculating an approximate value by substituting π with 3.14 or using any numerical approximation for pi.