The distance between a and n is |a - b| = |b - a|.
Using the definition given above, rewrite the statement using absolute value.
The distance between x^3 and -1 is at most 0.001.
The distance between x^3 and -1 is | x^3 + 1|.
The |x^3 + 1| is at most 0.001 can be expressed as
|x^3 + 1| is < or = 0.001.
Why must we set |x^3 + 1| to be less than or equal to 0.001and not greater than or equal to 0.001?