Question

What is the circumference of a circle whose area is 100
`\pi`?

A) 10 B) 20 C) 10
`\pi` D) 20
`\pi`E) 25
`\pi`

Answer 1

`S=100\pi\\\\ \pi r^2=100\pi \ |:\pi\\\\ r^2=100 \\\\ r=√(100) \ , \ r > 0\\\\ r=10\\\\ C=2\pi r=2\pi \cdot 10=20\pi`