Across
1
Difference between highest and lowest values
2
Collection of distinct elements
5
Single numeral from 0 to 9
6
Total distance around a shape
7
Number greater than zero
9
Proven mathematical statement
14
Line crossing from corner to corner
Down
2
Steepness of a line
3
Three-sided polygon
4
Line touching circle at one point
8
Result of addition
10
Symbol representing unknown value
11
Math using letters for unknown values
12
Line segment connecting two circle points
13
The number representing nothing