Tìm x trong các tỉ lệ thức sau
a) x-6 /x+4= 2/7
b) ( x+5) : \(2\frac{1}{2}\)= 40:(x+5)
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LH
28 tháng 9 2017
a) \(\frac{x-1}{x+5}=\frac{6}{7}\)
7( x - 1 ) = 6( x + 5 )
7x - 7 = 6x - 30
7x - 6x = -30 + 7
x = -23
b) \(\frac{x^2}{6}=\frac{24}{25}\)
\(x^2.25=6.24\)
\(x^2.25=144\)
\(x^2=\frac{144}{25}\)
\(x=\sqrt{\frac{144}{25}}\)
\(x=\frac{12}{5}\)
c) \(\frac{x-2}{x-4}=\frac{x+4}{x+7}\)
\(\left(x-2\right)\left(x+7\right)=\left(x+4\right)\left(x-4\right)\)
\(x^2+7x-2x-14=x^2-4x+4x-16\)
\(x^2+5x-14=x^2^{ }-16\)
\(x^2-x^2+5x=-16+14\)
\(5x=-2\)\(x=\frac{-2}{5}\)
12 tháng 11 2016
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) \(\frac{x}{0,16}=\frac{9}{x}\Rightarrow x^2=9.0,16=1,44\Rightarrow x=\pm1,2\)
17 tháng 8 2016
a) \(\left(\frac{1}{3}.x\right):\frac{2}{3}=\frac{7}{4}:\frac{2}{5}\)
\(\left(\frac{1}{3}.x\right):\frac{2}{3}=\frac{35}{8}\)
\(\Rightarrow\frac{1}{3}.x=\frac{35}{8}.\frac{2}{3}\)
\(\Rightarrow\frac{1}{3}.x=\frac{35}{12}\)
\(\Rightarrow x=\frac{35}{12}:\frac{1}{3}\)
\(\Rightarrow x=\frac{35}{4}\)
Vậy \(x=\frac{35}{4}\)
NH
0
23 tháng 7 2016
\(\frac{1}{3}x:\frac{2}{3}=1\frac{3}{4}:\frac{2}{5}\)
\(\Rightarrow\frac{1}{3}x:\frac{2}{3}=\frac{35}{8}\)
\(\Rightarrow\frac{1}{3}x=\frac{35}{12}\)
\(\Rightarrow x=\frac{35}{4}\)
23 tháng 7 2016
a) \(\left(\frac{1}{3}\cdot x\right):\frac{2}{3}=1\frac{3}{4}:\frac{2}{5}\)
\(=\left(\frac{1}{3}\cdot x\right):\frac{2}{3}=\frac{35}{8}\)
\(\Rightarrow\frac{1}{3}\cdot x=\frac{35}{8}\cdot\frac{2}{3}\)
\(\Rightarrow x=\frac{35}{12}:\frac{1}{3}=\frac{35}{4}\)
b) \(4,5:0,3=2,5:\left(0,1\cdot x\right)\)
\(=15=2,5:\left(0,1\cdot x\right)\)
\(\Rightarrow0,1\cdot x=2,25:15\)
\(\Rightarrow x=\frac{3}{20}:0,1=\frac{3}{2}=1,5\)
c) \(8:\left(\frac{1}{4}\cdot x\right)=2:0,02\)
\(8:\left(\frac{1}{4}\cdot x\right)=100\)
\(\Rightarrow\frac{1}{4}\cdot x=8:100\)
\(\Rightarrow x=\frac{2}{25}:\frac{1}{4}=\frac{8}{25}=0,32\)
d) \(3:2\frac{1}{4}=\frac{3}{4}:\left(6\cdot x\right)\)
\(=\frac{4}{3}=\frac{3}{4}:\left(6:x\right)\)
\(\Rightarrow6\cdot x=\frac{3}{4}:\frac{4}{3}\)
\(\Rightarrow x=\frac{9}{16}:6=\frac{3}{32}=0,09375\)
HT
5
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 : \(x+5=-4\Leftrightarrow x=-9\)