20:x=-12:15=? -15:35=27:x=? -8:5=x:3 -1:(-x)=7:6 sos cứu bé

`20:x = - 12:15`

`=> 20/x = -12/15`

`=> 20/x = -4/5`

`=> -4x = 20.5`

`=> -4x=100`

`=> x = 100:(-4)`

`=> x = - 25`

Vậy `x=-25`

`------------`

`-15:35 = 27:x`

`=> -15/35 = 27/x`

`=> -3/7 = 27/x`

`=> -3x = 27.7`

`=> -3x=189`

`=> x = 189:(-3)`

`=> x = -63`

Vậy `x=-63`

`-------------`

`-8:5=x:3`

`=> -8/5 = x/3`

`=> 5x = -8. 3`

`=> 5x = -24`

`=> x = -24/5`

Vậy `x=-24/5`

`-------------`

`-1:(-x) = 7:6`

`=> 1:x = 7:6`

`=> 1/x = 7/6`

`=> 7x = 6`

`=> x = 6/7`

Vậy `x = 6/7`

`-------------`

`***` Áp dụng: `a/b = c/d => ad = bc`

`color{green}{~green~}`