Across
1
Symbol representing unknown value
5
Exact correspondence on both sides
6
Single numeral from 0 to 9
8
Rectangle with four equal sides
9
Steepness of a line
11
Collection of distinct elements
12
System of ordered marks for measuring
Down
2
Part of a whole number
3
Value that does not change
4
Sum divided by count
5
Result of addition
7
Number less than zero
10
Longest side of a right triangle
13
Number greater than zero