Question

(ab - 9)(ab + 8) Please answer.

Answer 1

$\text{Use FOIL method:}\ (a+b)(c+d)=ac+ad+bc+bd\\\\(ab-9)(ab+8)=(ab)(ab)+(ab)(8)+(-9)(ab)+(-9)(8)\\\\=a^2b^2+8ab-9ab-72\\\\=\boxed{a^2b^2-ab-72}$