The 2 vertical lines about the letters mean ' the absolute value of' . That is if a or b have negative values then the absolute value will be the positive . For example if a = -4 then |a| = 4. The absolute value is always positive.
Therefore, for example, if a is 2 and b = -2 then |a| will be equal to |b|, because they both have a value of 2.
The vertical bars are the symbol for "absolute value", so the equation is saying, "the absolute value of 'a' is equal to the absolute value of 'b'." The absolute value is the magnitude of a number, so, for example, |-3| = 3.
If the magnitudes of two numbers are the same, they may be the same value, or they may differ in sign.
