Question

помогите пожалуйста

Answer 1

$\frac{9ab}{a+9b}( \frac{a}{9b}- \frac{9b}{9} )= \frac{9ab}{a+9b} \frac{a-9 b^{2} }{9b} = \frac{a}{a+9b} \frac{a-9 b^{2}}{1} = \frac{a(a-9 b^{2})}{a+9b}$