`#Sad`
`4B`
`a)`
`i,`
`1,8 : 1,3 = -2,7 : 5x`
`⇔ (1,8)/(1,3) = (-2,7)/(5x)`
`⇔ 1,8. 5x = (-2,7). 1,3`
`⇔ 9x = -3,51`
`⇔ x = -0,39`
`\text{Vậy}` `x=-0,39`
`ii,`
`15 : 4 = x : 3,5`
`⇔ (15)/4 = x/(3,5)`
`⇔ 15. 3,5 = 4x`
`⇔ 52,5 = 4x`
`⇔ x = 13,125`
`\text{Vậy}` `x=13,125`
`iii,`
`x : 6,5 = 0,13 : 0,25`
`⇔ x/(6,5) = (0,13)/(0,25)`
`⇔ 0,25x = 6,5. 0,13`
`⇔ 0,25x = 0,845`
`⇔ x = 3,38`
`\text{Vậy}` `x=3,38`
`iv,`
`5,25 : x = 3,6 : 2,4`
`⇔ (5,25)/x = (3,6)/(2,4)`
`⇔ 5,25. 2,4 = 3,6x`
`⇔ 12,6 = 3,6x`
`⇔ x = 3,5`
`\text{Vậy}` `x=3,5`
`b)`
`i,`
`x/4 = 9/(10)`
`⇔ 10x = 9. 4`
`⇔ 10x = 36`
`⇔ x = 3,6`
`\text{Vậy}` `x=3,6`
`ii,`
`x/(24) = 6/x`
`⇔ x. x = 6. 24`
`⇔ x^2 = 144`
`⇔` \(\left[ \begin{array}{l}x=12\\x=-12\end{array} \right.\)
`\text{Vậy}` `x=12` `\text{hoặc}` `x=-12`
`iii,`
`(5-2x)/3 = (4x-1)/-5`
`⇔ -5(5-2x) = 3(4x-1)`
`⇔ -25+10x = 12x-3`
`⇔ 10x-12x = 25-3`
`⇔ -2x = 22`
`⇔ x = -11`
`\text{Vậy}` `x=-11`
`iv,`
`(10-2x)/6 = 27/(5-x)`
`⇔ (2(5-x))/6 = 27/(5-x)`
`⇔ (5-x)/3 = 27/(5-x)`
`⇔ (5-x)(5-x) = 27. 3`
`⇔ 25-5x-5x+x^2 = 81`
`⇔ x^2-10x+25-81 = 0`
`⇔ x^2-10x-56 = 0`
`⇔ x^2+4x-14x-56 = 0`
`⇔ (x^2+4x)-(14x+56) = 0`
`⇔ x(x+4)-14(x+4) = 0`
`⇔ (x-14)(x+4) = 0`
`⇔` \(\left[ \begin{array}{l}x-14=0\\x+4=0\end{array} \right.\)
`⇔` \(\left[ \begin{array}{l}x=14\\x=-4\end{array} \right.\)
`\text{Vậy}` `x=14` `\text{hoặc}` `x=-4`
