[tex] \frac{a}{b} = \frac{c}{d}= \frac{2}{1} \\ Deci : \frac{a}{b} =2 =\ \textgreater \ a=2b \\ si : \frac{c}{d} =2 =\ \textgreater \ c=2d \\ \frac{a}{b}= \frac{c}{d} =\ \textgreater \ ad=bc \\ Stim : a*b*c*d=900=\ \textgreater \ 2b*b*2d*d=900 =\ \textgreater \ 3b*3d=900 =\ \textgreater \ [/tex]
9bd=900 bd=100
a*c*(b*d) =900 => ac= 900:100 ac=9
