a, \(\frac{x-6}{x+4}=\frac{2}{7}\Rightarrow7x-42=2x+8\)ĐK : \(x\ne-4\)

\(\Leftrightarrow5x=50\Leftrightarrow x=10\)(tm)

b, \(\left(x+5\right):2\frac{1}{2}=\frac{40}{x+5}\)ĐK : \(x\ne-5\)

\(\Leftrightarrow\frac{5\left(x+5\right)}{2}=\frac{40}{x+5}\Rightarrow5\left(x+5\right)^2=80\Leftrightarrow\left(x+5\right)^2=16\)

TH1 : \(x+5=4\Leftrightarrow x=-1\)

TH2 : \(x+5=-4\Leftrightarrow x=-9\)

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Chỗ 1/3/4 í

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Gỉai:

a, x=0,5

b,55/6

$-\dfrac{3}{x-2} = \dfrac45$

$4(x-2) = (-3).5$

$4x - 8 = -15$

$x = -\dfrac74$

\(\dfrac{-3}{x-2}=\dfrac{4}{5}\\ =>\left(x-2\right)\cdot4=-3\cdot5\\ =>\left(x-2\right)\cdot4=-15\\ =>x-2=-15:4\\ =>x-2=-3,75\\ =>x=-3,75+2\\ =>x=-1,75\)

a) \(\frac{3x-2}{1\frac{2}{5}}=\frac{2\frac{3}{7}}{2\frac{3}{5}}\Rightarrow3x-2=1.\frac{2}{5}.\frac{2\frac{3}{7}}{2\frac{3}{5}}=\frac{7}{5}.\frac{17}{7}.\frac{5}{13}\)

\(3x-2=\frac{17}{13}\Rightarrow3x=2+\frac{17}{13}=\frac{43}{13}\Rightarrow x=\frac{43}{39}.\)

b) \(\frac{x}{0,16}=\frac{9}{x}\Rightarrow x^2=9.0,16=1,44\Rightarrow x=\pm1,2\)

Lời giải:

a.

$x:27=-2:3,6=\frac{-5}{9}$

$x=27.\frac{-5}{9}=-15$

b.

$\frac{2x+1}{-27}=\frac{-3}{2x+1}$

$\Rightarrow (2x+1)^2=(-27)(-3)=81=9^2=(-9)^2$

$\Rightarrow 2x+1=9$ hoặc $2x+1=-9$

$\Rightarrow x=4$ hoặc $x=-5$