The variable substitution approach also eliminates
errors that commonly result when the coefficient
of x is negative. Students read problems in
the form |b – Ax| > c as they would those in the
form |Ax – b | > c—that is, as “Ax is farther than c
units away from b.” They also realize that because
Ax + b = b + Ax by the commutative property of
addition, |b + Ax| < c and |Ax + b| < c may both be
understood as the values of Ax that are closer than
c units from –b. The appendix (p. 598) provides
practice in solving absolute value inequalities when
the coefficient of x is not equal to 1.