Question

how do you write, x is 9 units from zero?

Answer 1

x is either x = 9 or x = -9

since those values are both 9 units away from 0

Answer 2

if you say x = 9 or x = -9, you can also say |x| = 9

Answer 3

This is because

|x| = k

turns into

x = k or x = -k

where k is some positive number

Answer 4

http://www.purplemath.com/modules/absolute.htm