Question

circumference and diameter
$c = 2\pi r$ and $c = \pi d$

1. if the diameter of a circle is 9 cm, what is the circumference?

1. if the diameter of a circle is 18 cm, what is the circumference?

1. if the diameter of a circle is 27 cm, what is the circumference?

$r = \frac{c}{2\pi}$ and $d = \frac{c}{\pi}$

1. if the circumference of a circle is 44 inches, what is the diameter?

1. if the circumference of a circle is 70 cm, what is the diameter?

1. if the circumference of a circle is 200 mm, what is the diameter?

Explanation:

Question 1

Step1: Identify the formula.

We use the formula for the circumference of a circle in terms of diameter, \( C=\pi d \), where \( d \) is the diameter. Here, \( d = 9\space\text{cm} \).

Step2: Substitute the value.

Substitute \( d = 9 \) into the formula \( C=\pi d \), we get \( C=\pi\times9 = 9\pi\space\text{cm} \).

Step1: Identify the formula.

We use the formula \( C = \pi d \), where \( d \) is the diameter. Here, \( d=18\space\text{cm} \).

Step2: Substitute the value.

Substitute \( d = 18 \) into \( C=\pi d \), we get \( C=\pi\times18=18\pi\space\text{cm} \).

Step1: Identify the formula.

We use the formula \( C=\pi d \), where \( d \) is the diameter. Here, \( d = 27\space\text{cm} \).

Step2: Substitute the value.

Substitute \( d=27 \) into \( C = \pi d \), we get \( C=\pi\times27 = 27\pi\space\text{cm} \).

Answer:

The circumference is \( 9\pi\space\text{cm} \) (or approximately \( 28.27\space\text{cm} \) if we take \( \pi\approx3.14 \)).

Question 2