Across
1
Longest side of a right triangle
2
Space between two intersecting lines
7
Total distance around a shape
9
Sum divided by count
11
Collection of distinct elements
12
Part of a line with two endpoints
13
Number divisible only by 1 and itself
Down
2
Reference line in a graph
3
The number representing nothing
4
Divisible by two
5
Closed shape with straight sides
6
Mathematical rule or equation
8
Repeated addition
10
Part of a circle's circumference
11
Rectangle with four equal sides