The absolute value is defined as
So for example, if <em>x</em> = 3, then |<em>x</em>| = |3| = 3, since 3 is positive. On the other hand, if <em>x</em> = -5, then |<em>x</em>| = |-5| = -(-5) = 5, since -5 is negative. The absolute value is always positive.
For the inequality |7 + 8<em>x</em>| > 5, you consider the two cases where the argument to the absolute value (the expression you find inside the bars) is either positive or negative.
• If 7 + 8<em>x</em> ≥ 0, then |7 + 8<em>x</em>| = 7 + 8<em>x</em>, so that
• Otherwise, if 7 + 8<em>x</em> < 0, then |7 + 8<em>x</em>| = -(7 + 8<em>x</em>), so that
The solution to the inequality is the union of these two intervals.