Across
1
Repeated addition
4
Line segment connecting two circle points
6
Reference line in a graph
7
Longest side of a right triangle
8
Three-sided polygon
9
Steepness of a line
12
Single numeral from 0 to 9
13
Part of a whole number
Down
2
Line crossing from corner to corner
3
Result of multiplication
5
Lines that never intersect
10
The number representing nothing
11
Symbol representing unknown value