Выполните деление (b/(18b-81)):(4b^2/(4b^2-81))
(b/(18b-81)):(4b^2/(4b^2-81))= (b(4b^2-81))/((18b-81)*4b^2)=(b(2b-9)(2b+9))/(9(2b-9)*4b^2)=(2b+9)/(36b)