12) (2a+3b−5)/a² − 5b/a² =

\(\frac{2a+3b-5}{a^2}-\frac{5b}{a^2}=\frac{2a+3b-5-5b}{a^2}=\frac{2a-2b-5}{a^2}\).

Ответ: \(\frac{2a-2b-5}{a^2}\)