Across
1
Sum divided by count
6
Symbol representing unknown value
7
Three-sided polygon
8
Number with digits after a point
9
Line touching circle at one point
12
Steepness of a line
Down
2
System of ordered marks for measuring
3
Lines that never intersect
4
Reference line in a graph
5
Difference between highest and lowest values
10
Math using letters for unknown values
11
Corner point of a polygon
13
Value that does not change