Recall the definition of absolute value:
• |x| = x if x ≥ 0
• |x| = -x if x < 0
So we have 2 cases to consider:
• If 4 - 3x ≥ 0, then |4 - 3x| = 4 - 3x, and we have
4 - 3x = 5x + 4
8x = 0
x = 0
• If 4 - 3x < 0, then |4 - 3x| = -(4 - 3x) = 3x - 4, which gives
3x - 4 = 5x + 4
2x = -8
x = -4
However, keep in mind that |x| is always non-negative. If x = -4, then the right side of the equation becomes
5(-4) + 4 = -20 + 4 = -16 < 0
so the solution in this case is extraneous.
