Question

1. what is the exact area of a circle with a diameter of 20 cm?

20π cm²
400π cm²
100π cm²
10π cm²

Explanation:

Step1: Find the radius

The diameter \( d = 20 \, \text{cm} \), and the radius \( r=\frac{d}{2}\). So \( r = \frac{20}{2}=10 \, \text{cm} \).

Step2: Use the area formula for a circle

The formula for the area of a circle is \( A=\pi r^{2} \). Substitute \( r = 10 \) into the formula: \( A=\pi\times(10)^{2}=100\pi \, \text{cm}^2 \).

Answer:

\( 100\pi \, \text{cm}^2 \) (corresponding to the option: \( 100\pi cm^{2} \))