Across
1
Line crossing from corner to corner
3
Total distance around a shape
5
Distance from center to edge of circle
6
Math using letters for unknown values
7
System of ordered marks for measuring
9
Repeated addition
10
Collection of distinct elements
12
Proven mathematical statement
13
Part of a line with two endpoints
Down
2
Sum divided by count
4
Part of a whole number
8
Three-sided polygon
11
Symbol representing unknown value