a,$\frac{-5}{x}$ = $\frac{-12}{7}$
Ta có: $\frac{-5}{x}$ = $\frac{-12}{7}$ => -5.7=-12.x hay -12.x=-5.7
=> -12.x= -35 => x= -35: (-12)= $\frac{35}{12}$
Vậy x= $\frac{35}{12}$
b, $\frac{x}{4}$ = $\frac{14}{x}$
Ta có:$\frac{x}{4}$ = $\frac{14}{x}$ => x.x=14.4 => 2.x=56 => x= 56:2= 28
Vậy x= 28
c, $\frac{x}{7}$ = $\frac{y}{16}$ và x-y= 36
Ta có $\frac{x}{7}$ = $\frac{y}{16}$ =>$\frac{x-y}{7-16}$ = $\frac{36}{-9}$ = -4
=> $\frac{x}{7}$ = -4 => x= -4.7 = -28
=> $\frac{y}{16}$ = -4 => y= -4.16 = -64
Vậy x= -28
y= -64