Across
1
Repeated addition
5
Value that does not change
6
Single numeral from 0 to 9
7
Round shape with all points equidistant
9
Steepness of a line
12
Difference between highest and lowest values
Down
2
Rectangle with four equal sides
3
Longest side of a right triangle
4
Three-sided polygon
8
Number that divides evenly into another
10
Number greater than zero
11
The number representing nothing
13
Result of raising a number to an exponent