Có bao nhiêu giá trị \(x\) thỏa mãn  \(\dfrac{{16}}{x} = \dfrac{x}{{25}}\)

\(a = c\)

\(a.c = b.d\)

\(a.d = b.c\)

\(b = d\)

\(\dfrac{5}{{35}} = \dfrac{9}{{63}}\)

\(\dfrac{{63}}{9} = \dfrac{{35}}{5}\)

\(\dfrac{{35}}{9} = \dfrac{{63}}{5}\)      

\(\dfrac{{63}}{{35}} = \dfrac{9}{5}\)

\(\dfrac{7}{{12}}\) và \(\dfrac{5}{6}:\dfrac{4}{3}\)

\(\dfrac{6}{7}:\dfrac{{14}}{5}\) và \(\dfrac{7}{3}:\dfrac{2}{9}\)

\(\dfrac{{15}}{{21}}\) và \( - \dfrac{{125}}{{175}}\)

\(\dfrac{{ - 1}}{3}\)  và \(\dfrac{{ - 19}}{{57}}\)      

\(\dfrac{2}{a} = \dfrac{5}{b}\)

\(\dfrac{b}{5} = \dfrac{2}{a}\)

\(\dfrac{2}{5} = \dfrac{a}{b}\)

\(\dfrac{2}{b} = \dfrac{5}{a}\)

\(x = \dfrac{1}{5}\)

\(x =  - \dfrac{5}{4}\)

\(x = \dfrac{5}{4}\)

\(x = \dfrac{4}{5}\)

\(x = \)\(\dfrac{{ - 4}}{3}\)  

\(x = 4\)

\(x =  - 12\)

\(x =  - 10\)