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