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

$$\begin{gathered} \mathrm{Câu} 1: \mathrm{Cho} \frac{\mathrm{a}}{\mathrm{b}} = \frac{\mathrm{c}}{\mathrm{d}}. \mathrm{Chứng} \mathrm{minh} \frac{\mathrm{a} - \mathrm{b}}{\mathrm{a}}= \frac{\mathrm{c} -\mathrm{d}}{\mathrm{c}} \\ \mathrm{Aii} \mathrm{nhanhh} \mathrm{mk} \mathrm{chấm} \mathrm{cho} 5\mathrm{đ}😇😇 \end{gathered}$$