Across
1
Longest side of a right triangle
2
Part of a line with two endpoints
5
Symbol representing unknown value
6
Amount of space an object occupies
11
Part of a circle's circumference
12
Exact correspondence on both sides
13
Sum divided by count
Down
2
Rectangle with four equal sides
3
Three-sided polygon
4
Value that does not change
7
Closed shape with straight sides
8
The number representing nothing
9
Number greater than zero
10
Number divisible only by 1 and itself