Question

1. 2.5 cm (with a circle diagram)

Explanation:

Assuming we need to find the circumference of the circle (since the radius \( r = 2.5 \, \text{cm} \) is given), we use the formula for the circumference of a circle \( C = 2\pi r \).

Step 1: Identify the radius

The radius \( r \) of the circle is given as \( 2.5 \, \text{cm} \).

Step 2: Use the circumference formula

The formula for the circumference \( C \) of a circle is \( C = 2\pi r \). Substitute \( r = 2.5 \, \text{cm} \) into the formula:
\[
C = 2 \times \pi \times 2.5
\]

Step 3: Calculate the value

First, multiply \( 2 \) and \( 2.5 \): \( 2 \times 2.5 = 5 \). Then, multiply by \( \pi \): \( C = 5\pi \, \text{cm} \). If we use \( \pi \approx 3.14 \), then \( C \approx 5 \times 3.14 = 15.7 \, \text{cm} \).

Answer:

If we use \( \pi \approx 3.14 \), the circumference is \( 15.7 \, \text{cm} \); in terms of \( \pi \), it is \( 5\pi \, \text{cm} \).