# Area of Circle

## Basic Concept

#### Area of a Circle

$$A = \pi\times r^2$$

$$\pi = \frac{22}{7} = 3.14$$

$$r = \text{radius}$$

$$A =\frac{1}{4} \pi\times d^2$$

$$\pi = \frac{22}{7} = 3.14$$

$$d = \text{diameter}$$

#### Area of a Sector

If $$\theta$$ is measured in degrees then:

$$\text{Area of sector} = \frac{\theta}{360^\circ}\times \text{area of circle}$$

$$\text{Area of sector} = \frac{\theta}{360^\circ}\times \pi\times r^2$$

If $$\theta$$ is measured in radians then:

$$\text{Area of sector} = \frac{1}{2}\times r^2 \times \theta$$

$$1 \pi \text { radians} = 180^\circ$$

$$1 \text{ radians ≈ 57.3°}$$