Test 4 Section 4 Number 24

Because the question tells you that segment AB is a diameter, you know that arc ADB is exactly half the circumference of the circle. If the length of the arc is 8π, therefore, the full circumference of the circle must be 16π.

How do we solve for the radius if we know the circumference? We use the formula for circumference (provided at the beginning of the section if you don’t have it memorized).

    \begin{align*}C&=2\pi r\\16\pi&=2\pi r\\16&=2r\\8&=r\end{align*}