Let's solve the problems shown in the third image, where we need to determine the circumference of the given circles.

Formula for Circumference

From the first image, we have two formulas:

• $C = \pi d$ (if diameter is given)
• $C = 2\pi r$ (if radius is given)

Solving the Problems

(a) Given diameter $d = 8$ cm

$C = \pi d = 3.14 \times 8 = 25.12 \text{ cm}$

(b) Given radius $r = 3.5$ m

$C = 2\pi r = 2 \times 3.14 \times 3.5 = 21.98 \text{ m}$

(c) Given radius $r = 7.2$ mm

$C = 2\pi r = 2 \times 3.14 \times 7.2 = 45.22 \text{ mm}$

Final Answers

• (a) 25.12 cm
• (b) 21.98 m
• (c) 45.22 mm

Would you like a step-by-step breakdown of how each calculation was done?

Here are five related questions to expand your understanding:

1. What is the relationship between the diameter and the radius of a circle?
2. How does increasing the radius affect the circumference?
3. Why is $\pi$ an irrational number?
4. How can we approximate $\pi$ for more precise calculations?
5. Can the circumference of a circle ever be a whole number?

Tip: If you remember that $d = 2r$, you can easily switch between the two formulas for circumference!