Question

I this equation correct?
If |m| = -18 then m = -18 and m = 18

Answer 1

No. |m| can only be positive.

Explanation:

Absolute value |m| indicates magnitude, i.e. it has no "direction". m=-18 indicates that m is 18 units left (negative) of position 0; it has direction. |m| asks for the value of m without any direction, i.e. its magnitude.

If it was: |m|=18 then the rest would be true.

See also magnitude vs vectors.