Ta có:$\frac{ab}{cd}$ =$\frac{ab.1001}{cd.1001}$ =$\frac{ab0ab}{cd0cd}$
⇒$\frac{ab}{cd}$ =$\frac{ab0ab}{cd0cd}$ .(đpcm)
VD:$\frac{12}{13}$ =$\frac{12.1001}{13.1001}$ =$\frac{12012}{13013}$ .
$\frac{13}{25}$ =$\frac{13.1001}{25.1001}$ =$\frac{13013}{25025}$ .