Across
1
Repeated addition
3
Line segment connecting two circle points
6
Number less than zero
8
Difference between highest and lowest values
9
Closed shape with straight sides
10
Lines that never intersect
12
Single numeral from 0 to 9
13
U-shaped curve of a quadratic function
Down
2
Rectangle with four equal sides
4
Line crossing from corner to corner
5
Three-sided polygon
7
Divisible by two
11
Symbol representing unknown value