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