Cho a/b = c/d. Chứng minh a / (a - b) = c / (c - d)

\(\frac{a}{b} = \frac{c}{d}\)

⇔\(\frac{b}{a} = \frac{d}{c}\)

⇔\(\frac{b}{a} = \frac{d}{c}\)

⇔\(1 - \frac{b}{a} = 1 - \frac{d}{c}\)

⇔\(\frac{{a - b}}{a} = \frac{{c - d}}{c}\)

⇔\(\frac{a}{{a - b}} = \frac{c}{{c - d}}\).