Across
1
The number representing nothing
3
Collection of distinct elements
5
Part of a line with two endpoints
6
Difference between highest and lowest values
7
Number less than zero
9
Single numeral from 0 to 9
12
Closed shape with straight sides
Down
2
Total distance around a shape
4
Mathematical statement of equality
8
Repeated addition
10
Proven mathematical statement
11
Corner point of a polygon