Đáp án:
Giải thích các bước giải:
a)$\frac{x}{9}$ =$\frac{5}{3}$
=>$\frac{x}{9}$=$\frac{5 x 3}{3 x 3}$
=>$\frac{x}{9}$=$\frac{15}{9}$
=> x=15
b) $\frac{17}{x}$=$\frac{85}{105}$
=>$\frac{17}{x}$=$\frac{85 : 5}{105 : 5}$
=> $\frac{17}{x}$=$\frac{17}{21}$
=> x=21
c) $\frac{6}{8}$=$\frac{15}{x}$
=> $\frac{6 : 2}{8 : 2}$=$\frac{15}{x}$
=>$\frac{3}{4}$=$\frac{15}{x}$
=>$\frac{3 x 5}{4 x 5}$=$\frac{15}{x}$
=>$\frac{15}{20}$=$\frac{15}{x}$
=> x=20
d) $\frac{x}{8}$+$\frac{2}{3}$=$\frac{7}{6}$
=> $\frac{x}{8}$=$\frac{7}{6}$-$\frac{2}{3}$
=> $\frac{x}{8}$= $\frac{1}{2}$
=> $\frac{x}{8}$= $\frac{1 x 4}{2 x 4}$
=> $\frac{x}{8}$= $\frac{4}{8}$
=>x= 4
