Don’t watch the clock; do what it does. Keep going. – **Sam Levenson**

1. Circumference of a circle = 2πr.

2. Area of a circle = πr^{2}.

3. Length of an arc of a sector of a circle with radius *r* and angle with degree measure θ is \frac{\theta}{360} \times 2 \pi r

4. Area of a sector of a circle with radius *r* and angle with degree measure θ is \frac{\theta}{360} \times \pi r^2

5. Area of segment of a circle = Area of the corresponding sector – Area of the corresponding triangle.