\(\frac{a+m}{b+m}=\frac{b\left(a+m\right)}{b\left(b+m\right)}=\frac{ab+bm}{b\left(b+m\right)};\frac{a}{b}=\frac{a\left(b+m\right)}{b\left(b+m\right)}=\frac{ab+am}{b\left(b+m\right)}\)
xét a<b \(\Rightarrow\frac{a+m}{b+m}>\frac{a}{b}\)
xét a=b \(\Rightarrow\frac{a+m}{b+m}=\frac{a}{b}\)
xét a>b \(\Rightarrow\frac{a+m}{b+m}