a) \(\frac{x}{27}=\frac{-2}{3,6}\Leftrightarrow x=\frac{-2.27}{3,6}=-15\)

b) \(\frac{4\frac{1}{4}}{2\frac{7}{8}}=\frac{x}{1,61}\Leftrightarrow\frac{4,25}{2,875}=\frac{x}{1,61}\Leftrightarrow x=\frac{4,25.1,61}{2,875}=2,38\)

a) \(\frac{x}{27}=-\frac{2}{3,6}\Rightarrow x=\frac{-2.27}{3,6}=-15\)

b) \(\frac{4\frac{1}{4}}{2\frac{7}{8}}=\frac{x}{1,61}\Rightarrow\frac{\frac{17}{4}}{\frac{23}{8}}=\frac{x}{1,61}\Leftrightarrow\frac{17}{4}\cdot\frac{8}{23}=\frac{x}{1,61}\)

 \(\frac{34}{23}=\frac{x}{1,61}\Rightarrow x=\frac{1,61.34}{23}=2,38\)

a, ta có:27:3,6=7,5

=>-2x7,5=15

vậy x cần tìm là 15

b, -0,52:x=\(-\frac{4}{7}\)

\(\frac{-13}{25}\): x=\(\frac{-4}{7}\)

x=\(\frac{-13}{25}:\frac{-4}{7}\)

x=0,91

a)\(\frac{x}{27}=\frac{-2}{3,6}\)

=>x.3,6=27.(-2)

=>x.3,6=-54

=>x=-15

b)-0,52:x=-9,36:16,38

=>-0,52:x=-4/7

=>x=0,91

c)\(\frac{4\frac{1}{4}}{2\frac{7}{8}}=\frac{x}{1,61}\)

=>\(2\frac{7}{8}.x=4\frac{1}{4}.1,61\)

=>\(2\frac{7}{8}.x=\frac{2737}{400}\)

=>x=\(\frac{119}{50}\)

a,\(\frac{x}{27}=-\frac{2}{3,6}\)

\(\Leftrightarrow x.3,6=27.-2\)

\(\Leftrightarrow x.3,6=-54\)

\(\Leftrightarrow x=-15\)

b,\(-0,52\div x=-9,36\div16,38\)

\(\Leftrightarrow-0,52\div x=-\frac{4}{7}\)

\(\Leftrightarrow x=\frac{91}{100}\)

c,\(\frac{4\frac{1}{4}}{2\frac{7}{8}}=\frac{x}{1,61}\)

\(\Leftrightarrow\frac{4,25}{2,875}=\frac{x}{1,61}\)

\(\Leftrightarrow x.2,875=4,25.1,61\)

\(\Leftrightarrow x.2,875=6,8425\)

\(\Leftrightarrow x=2,38\)

Bài 1a:

\(\frac{4,6}{1,4}\) = \(\frac{11,5}{5x}\)

4,6 x 5\(x\) = 11,5 x 1,4

23\(x\) = 16,1

\(x\) = 16,1 : 23

\(x\) = 0,7

Vậy \(x\) = 0,7

Bài 1b:

\(\frac{x^2}{6}\) = \(\frac{24}{25}\)

25\(x^2\) = 24.6

25\(x^2\) = 144

\(x^2\) = 144/25

\(x\) = - 12/5 hoặc \(x\) = 12/5

Vậy \(x\) ∈ {-12/5; 12/5}

Bài 1c:

\(\frac{x+2}{2}\) = \(\frac{1}{1-x}\)

(\(x\) + 2)(1 - \(x\)) = 1.2

\(x\) - \(x^2\) + 2 - 2\(x\) = 2

\(x^2\) + (2\(x\) - \(x\)) + 2 - 2 = 0

\(x^2\) + \(x\) + 0 = 0

\(x\)(\(x\) + 1) = 0

\(x\) = 0

\(x\) + 1 = 0

\(x\) = - 1

Vậy \(x\) ∈ {-1; 0}

Bài 2: 

a) \(\frac{x}{-27}=\frac{-3}{x}\Leftrightarrow-\frac{x}{27}=-\frac{3}{x}\Leftrightarrow-x.x=\left(-27\right).\left(-3\right)\Leftrightarrow-x^2=-81\Leftrightarrow\orbr{\begin{cases}x=9\\x=-9\end{cases}}\)

\(\Rightarrow\orbr{\begin{cases}x=9\\x=-9\end{cases}}\)

b) \(\frac{-9}{x}=\frac{-x}{\frac{4}{49}}\Leftrightarrow-\frac{9}{x}=-\frac{49x}{4}\Leftrightarrow-9.4=-x.49x\Leftrightarrow-36=-49x^2\Leftrightarrow\orbr{\begin{cases}x=\frac{6}{7}\\x=-\frac{6}{7}\end{cases}}\)

\(\Rightarrow\orbr{\begin{cases}x=\frac{6}{7}\\x=-\frac{6}{7}\end{cases}}\)

D nha bạn

thanks

1. Theo t/c của dãy tỉ số bằng nhau ta có : 

\(\frac{x}{2}=\frac{y}{5}=\frac{x.y}{2.5}=\frac{90}{10}=9\)

\(\frac{x}{2}=9\Rightarrow x=9.2=18\)

\(\frac{y}{5}=9\Rightarrow y=9.5=45\)

Vậy x = 18 ; y = 45 

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