Circumference and Area of Circles Worksheets - Free Printable

To solve the problem of finding the area of each circle, we need to use the formula for the area of a circle:

\[
\text{Area} = \pi r^2
\]

where \( r \) is the radius of the circle. If the diameter \( d \) is given instead of the radius, we can find the radius using the relationship:

\[
r = \frac{d}{2}
\]

Let's go through each circle step by step.

---

Circle 1:

- Diameter (\( d \)) = 4 cm
- Radius (\( r \)) = \(\frac{d}{2} = \frac{4}{2} = 2\) cm
- Area = \(\pi r^2 = \pi (2)^2 = 4\pi\) square cm

Answer: \( 4\pi \) square cm

---

Circle 2:

- Diameter (\( d \)) = 6 cm
- Radius (\( r \)) = \(\frac{d}{2} = \frac{6}{2} = 3\) cm
- Area = \(\pi r^2 = \pi (3)^2 = 9\pi\) square cm

Answer: \( 9\pi \) square cm

---

Circle 3:

- Diameter (\( d \)) = 8 cm
- Radius (\( r \)) = \(\frac{d}{2} = \frac{8}{2} = 4\) cm
- Area = \(\pi r^2 = \pi (4)^2 = 16\pi\) square cm

Answer: \( 16\pi \) square cm

---

Circle 4:

- Diameter (\( d \)) = 10 cm
- Radius (\( r \)) = \(\frac{d}{2} = \frac{10}{2} = 5\) cm
- Area = \(\pi r^2 = \pi (5)^2 = 25\pi\) square cm

Answer: \( 25\pi \) square cm

---

Circle 5:

- Diameter (\( d \)) = 12 cm
- Radius (\( r \)) = \(\frac{d}{2} = \frac{12}{2} = 6\) cm
- Area = \(\pi r^2 = \pi (6)^2 = 36\pi\) square cm

Answer: \( 36\pi \) square cm

---

Circle 6:

- Diameter (\( d \)) = 14 cm
- Radius (\( r \)) = \(\frac{d}{2} = \frac{14}{2} = 7\) cm
- Area = \(\pi r^2 = \pi (7)^2 = 49\pi\) square cm

Answer: \( 49\pi \) square cm

---

Circle 7:

- Diameter (\( d \)) = 16 cm
- Radius (\( r \)) = \(\frac{d}{2} = \frac{16}{2} = 8\) cm
- Area = \(\pi r^2 = \pi (8)^2 = 64\pi\) square cm

Answer: \( 64\pi \) square cm

---

Circle 8:

- Diameter (\( d \)) = 18 cm
- Radius (\( r \)) = \(\frac{d}{2} = \frac{18}{2} = 9\) cm
- Area = \(\pi r^2 = \pi (9)^2 = 81\pi\) square cm

Answer: \( 81\pi \) square cm

---

Circle 9:

- Diameter (\( d \)) = 20 cm
- Radius (\( r \)) = \(\frac{d}{2} = \frac{20}{2} = 10\) cm
- Area = \(\pi r^2 = \pi (10)^2 = 100\pi\) square cm

Answer: \( 100\pi \) square cm

---

Final Answers:

\[
\boxed{
\begin{array}{ccc}
\text{Circle 1: } & 4\pi \text{ square cm} \\
\text{Circle 2: } & 9\pi \text{ square cm} \\
\text{Circle 3: } & 16\pi \text{ square cm} \\
\text{Circle 4: } & 25\pi \text{ square cm} \\
\text{Circle 5: } & 36\pi \text{ square cm} \\
\text{Circle 6: } & 49\pi \text{ square cm} \\
\text{Circle 7: } & 64\pi \text{ square cm} \\
\text{Circle 8: } & 81\pi \text{ square cm} \\
\text{Circle 9: } & 100\pi \text{ square cm} \\
\end{array}
}
\]