Chapter 10 Circles

Notes

Circles:

Circle is collection of points at equal distance from center

Important terms:

Radius → line from center to circle

Diameter → twice radius

Chord → line joining two points on circle

Tangent → touches circle at one point

Secant → cuts circle at two points

Important theorems:

Tangent is perpendicular to radius

Tangents from external point are equal

Formulas:

Diameter:

d=2r

Circumference:

C=2πr

r

d=2r≈6.00

C=2πr≈18.85

circumference

r = 3.00

Area:

A=πr

2

r

A=πr

2

≈28.27

C=2πr≈18.85

r = 3.00

Important points:

Diameter is longest chord

Radius and tangent angle = 90°

Common mistakes:

Confusing radius and diameter

Wrong π value

Forgetting square in area