Hoàng Thị Thanh Trúc

a,

\(\frac{x}{7}=\frac{6}{21}\Rightarrow x=\frac{6.7}{21}=2\)

b,

\(\frac{-5}{y}=\frac{20}{28}\Rightarrow y=\frac{\left(-5\right).28}{20}=-7\)

a. -13

b.-7

bài 2 :

a. x=2

b. y=-7

c. x=5

\(\frac{x}{7}=\frac{6}{21}\Rightarrow x=\frac{6.7}{21}=\frac{42}{21}=2\)

\(-\frac{5}{y}=\frac{20}{28}\Rightarrow y=-\frac{5.28}{20}=-\frac{140}{20}=-7\)

\(\frac{2}{7}=\frac{6}{21}\)

\(\frac{-5}{-7}=\frac{5}{7}=\frac{20}{28}\)

\(\frac{6}{11}x=\frac{9}{2}y=\frac{18}{5}z\Rightarrow\frac{6x}{11.18}=\frac{9y}{2.18}=\frac{18z}{5.18}\)

\(\Rightarrow\frac{-x}{-33}=\frac{y}{4}=\frac{z}{5}=\frac{-x+y+z}{-33+4+5}=\frac{-120}{-24}=5\)

\(\Rightarrow x=165;y=20;z=25\)

Ta có ; \(\frac{2}{x}=\frac{x}{8}\)

\(\Leftrightarrow x^2=2.8\)

\(\Leftrightarrow x^2=16\)

\(\Rightarrow x=\left\{-4;4\right\}\)

b y=-7

a x=4

c y=

\(\frac{3}{7}=\frac{y}{21}\Rightarrow y=\frac{3\times21}{7}=9\)

\(\frac{3}{x-5}=\frac{-4}{x+2}\)

\(\Leftrightarrow3.\left(x+2\right)=-4\left(x-5\right)\)

\(\Leftrightarrow3x+6=-4x+20\)

\(\Leftrightarrow3x+4x=20-6\)

\(\Leftrightarrow7x=14\)

\(\Leftrightarrow x=2\)

Cảm ơn

-xx=-2x4

-xx=-8

xx=8

x²=8

x= căn bâc của 8

a; \(\dfrac{-x}{4}\) = \(\dfrac{-2}{x}\)

    -\(x.x\) = -2.4

    -\(x^2\) = -8

      \(x^2\) = 8

      \(\left[{}\begin{matrix}x=-\sqrt{8}\\x=\sqrt{8}\end{matrix}\right.\)

Vậy \(x\in\) {-\(\sqrt{8}\); \(\sqrt{8}\)}

\(\text{3 Giải}\)

\(\frac{x+1}{6}=\frac{8}{3}=\frac{16}{6}\Rightarrow x+1=16\Rightarrow x=15.\text{Vậy: x=15}\)