Chapter 12 Areas Related to Circles

Notes

Areas Related to Circles:

This chapter deals with area and perimeter of parts of a circle.

Important formulas:

Area of Circle:

A=πr

2

r

A=πr

2

≈28.27

C=2πr≈18.85

r = 3.00

Circumference:

C=2πr

r

d=2r≈6.00

C=2πr≈18.85

circumference

r = 3.00

Area of Sector:

360

∘

θ

​

πr

2

Length of Arc:

360

∘

θ

​

⋅2πr

Area of Ring:

π(R

2

−r

2

)

Special shapes:

Semicircle = Half circle

Quadrant = One-fourth circle

Sector = Portion of circle enclosed by two radii and an arc

Important points:

Use π = 22/7 unless stated otherwise

Convert diameter to radius first

θ = central angle

Common mistakes:

Forgetting to divide by 360°

Using diameter instead of radius

Missing square on radius