a) Ta có: \(\frac{a}{b}=\frac{c}{d}\) \(\Rightarrow\frac{a}{b}+1=\frac{c}{d}+1\Leftrightarrow\frac{a+b}{b}=\frac{c+d}{d}\)
b Ta có: \(\frac{a}{b}=\frac{c}{d}\)\(\Rightarrow\frac{a}{c}=\frac{b}{d}=\frac{a-b}{c-d}\)
Từ \(\frac{a}{c}=\frac{a-b}{c-d}\) \(\Rightarrow\frac{a}{a-b}=\frac{c}{c-d}\)