Across
1
Part of a circle's circumference
2
Number divisible only by 1 and itself
3
Space between two intersecting lines
5
Longest side of a right triangle
7
Three-sided polygon
9
Line crossing from corner to corner
11
Corner point of a polygon
Down
2
Parts per hundred
4
Math using letters for unknown values
6
U-shaped curve of a quadratic function
8
The number representing nothing
9
Single numeral from 0 to 9
10
Closed shape with straight sides