d = 2r
d  = r
2
c = 2 pi r
c = pi d
A = area

- all numbers ending in 0 or 5

- the sum of the digits is divisible by 9.

Perpendicular Bisector-Separated into 2 equal parts.

Formulas

Formulas, d = diameter, r = radius, c = circumference, A = Area


d = 2r
d  = r
2
c = 2 pi r
c = pi d
A = area

The Divisible Rule for 9

9.

- the sum of the digits is divisible by 9.

eg. 1+8+9+7+2+3+6 = 36
3+6 = 9

The Divisibility Rule for 5

5.

- all numbers ending in 0 or 5

eg. 5, 10 , 15, 20, 25, 30, 35, 40