## Intermediate Algebra (12th Edition)

The inverse property of multiplication holds that $a\times\frac{1}{a}=1$ (for some real number $a$). Therefore, $-\frac{9}{8}(-\frac{8}{9})=-\frac{9}{8}\times-\frac{8}{9}=\frac{9\times8}{8\times9}=\frac{72}{72}=1$.