Bài 8 :
a, $\dfrac{x}{5}$ = $\dfrac{6}{-10}$
⇒ x = $\text{-3}$
Ta có : $\text{-10x = 5 . 6}$
⇔ $\text{-10x = 30}$
⇔ $\text{x = 30 : ( -10 )}$
⇔ $\text{-3}$

b, $\dfrac{3}{x}$ = $\dfrac{-33}{77}$
⇒ x = $\text{-7}$
Ta có : $\text{-3x = 77 . 3}$
⇔ $\text{-3x = 231}$
⇔ $\text{x = 231 : ( -3 )}$
⇔ $\text{-7}$

c, $\dfrac{x}{2}$ = $\dfrac{8}{x}$
⇒ x = $\text{4}$
Ta có : $\text{x . x = 8 . 2}$
⇔ $\text{$x^2$ = 16}$
⇔ $\text{$x^2$ = $4^2$}$
⇔ $\text{4}$

d, $\dfrac{x}{3}$ = $\dfrac{-12}{x}$
⇒ x vô lí
Ta có : $\text{x . x = -12 . 3}$
⇔ $\text{$x^2$ = -36}$
⇔ x vô lí.

f, $\dfrac{-4}{8}$ = $\dfrac{x}{-10}$ = $\dfrac{-7}{x}$ = $\dfrac{z}{-24}$
⇒ x = $\text{5}$ ; y = $\text{14}$ ; z = $\text{12}$
Ta có : $\dfrac{-4}{8}$ = $\dfrac{x}{-10}$
⇔ $\text{8x = ( -4 ) . ( -10 )}$
⇔ $\text{8x = 40}$
⇔ $\text{x = 40 : 8}$
⇔ $\text{x = 5}$

$\dfrac{5}{-10}$ = $\dfrac{-7}{y}$
⇔ $\text{5y = ( -10 ) . ( -7 )}$
⇔ $\text{5y = 70}$
⇔ $\text{y = 70 : 5}$
⇔ $\text{y = 14}$

$\dfrac{-7}{14}$ = $\dfrac{-z}{24}$
⇔ $\text{14z = ( -7 ) . ( -24 )}$
⇔ $\text{14z = 168}$
⇔ $\text{z = 168 : 14}$
⇔ $\text{z = 12}$

g, $\dfrac{-3}{6}$ = $\dfrac{x}{-2}$ = $\dfrac{-18}{y}$ = $\dfrac{z}{-24}$
⇒ x = $\text{1}$ ; y = $\text{36}$ ; z = $\text{12}$
Ta có : $\dfrac{-3}{6}$ = $\dfrac{x}{-2}$
⇔ $\text{6x = ( -3 ) . ( -2 )}$
⇔ $\text{6x = 6}$
⇔ $\text{x = 6 : 6}$
⇔ $\text{x = 1}$

$\dfrac{1}{-2}$ = $\dfrac{-18}{y}$
⇔ $\text{1y = ( -18 ) . ( -2 )}$
⇔ $\text{1y = 36}$
⇔ $\text{y = 36 : 1}$
⇔ $\text{y = 36}$

$\dfrac{-18}{36}$ = $\dfrac{z}{-24}$
⇔ $\text{36z = ( -18 ) . ( -24 )}$
⇔ $\text{36z = 432}$
⇔ $\text{z = 432 : 36}$
⇔ $\text{z = 12}$

h, $\dfrac{-3}{6}$ = $\dfrac{x}{-2}$ = $\dfrac{-18}{y}$ = $\dfrac{z}{-24}$
⇒ x = $\text{1}$ ; y = $\text{36}$ ; z = $\text{12}$
Ta có : $\dfrac{-3}{6}$ = $\dfrac{x}{-2}$
⇔ $\text{6x = ( -3 ) . ( -2 )}$
⇔ $\text{6x = 6}$
⇔ $\text{x = 6 : 6}$
⇔ $\text{x = 1}$

$\dfrac{1}{-2}$ = $\dfrac{-18}{y}$
⇔ $\text{1y = ( -18 ) . ( -2 )}$
⇔ $\text{1y = 36}$
⇔ $\text{y = 36 : 1}$
⇔ $\text{y = 36}$

$\dfrac{-18}{36}$ = $\dfrac{z}{-24}$
⇔ $\text{36x = ( -18 ) . ( -24 )}$
⇔ $\text{36x = 432}$
⇔ $\text{x = 432 : 36}$
⇔ $\text{x = 12}$

k, $\dfrac{-24}{-6}$ = $\dfrac{x}{3}$ = $\dfrac{4}{y^2}$ = $\dfrac{z^3}{-2}$
⇒ x = $\text{12}$ ; y = $\text{1}$ ; z = $\text{-2}$
Ta có : $\dfrac{-24}{-6}$ = $\dfrac{x}{3}$
⇔ $\text{-6x = ( -24 ) . 3}$
⇔ $\text{-6x = -72}$
⇔ $\text{x = (-72 ) : ( -6 )}$
⇔ $\text{x = 12}$

$\dfrac{12}{3}$ = $\dfrac{4}{y^2}$
⇔ $\text{12$y^2$= 4 . 3}$
⇔ $\text{12$y^2$ = 12}$
⇔ $\text{$y^2$ =12 : 12}$
⇔ $\text{$y^2$ = 1}$
⇔ $\text{$y^2$ = $1^2$}$
⇔ $\text{y = 1}$

$\dfrac{4}{1}$ = $\dfrac{z^3}{-2}$
⇔ $\text{1$z^3$ = ( -2 ) . ( 4 )}$
⇔ $\text{1$z^3$ = -8}$
⇔ $\text{$z^3$ = -8 : 1}$
⇔ $\text{$z^3$ = -8 }$
⇔ $\text{$z^3$ = $-2^3$}$
⇔ $\text{z = -2}$

n, $\dfrac{x}{3}$ = $\dfrac{7}{y}$
⇒ x và y = $\sqrt{21}$
Ta có : $\text{x . y = 7 . 3}$
⇔ $\text{x . y = 21}$
⇔ x và y = $\sqrt{21}$

m, $\dfrac{2}{x}$ = $\dfrac{y}{-3}$
⇒ x và y vô lí
Ta có : $\text{x . y = -3 . 2}$
⇔ $\text{x . y = -6}$
⇔ x và y = $\sqrt{21}$ vì -6 ko có căn bậc 2.

Câu e không đầy đủ ảnh nên mình xin phép không làm ạ . Câu h giống y hệt câu f , câu l mik k biết làm ạ !

         ~ Chúc tus học tốt nhé ~

Đây em, có vài câu chị không làm được
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