Tìm x :
\(\frac{7}{x-1}=\frac{x+1}{8}\) .
K
Khách
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DA
2
30 tháng 4 2016
\(\frac{x+1}{5}+\frac{x+1}{6}=\frac{x+1}{7}+\frac{x+1}{8}\)
\(\Rightarrow\frac{x+1}{5}+\frac{x+1}{6}-\frac{x+1}{7}-\frac{x+1}{8}=0\)
\(\Rightarrow\left(x+1\right)\cdot\frac{1}{5}+\left(x+1\right)\cdot\frac{1}{6}-\left(x+1\right)\cdot\frac{1}{7}-\left(x+1\right)\cdot\frac{1}{8}=0\)
\(\Rightarrow\left(x+1\right)\cdot\left(\frac{1}{5}+\frac{1}{6}-\frac{1}{7}-\frac{1}{8}\right)=0\)
\(\Rightarrow\left(x+1\right)\cdot\frac{293}{840}=0\)
\(\Rightarrow x+1=0\)
\(\Rightarrow x=-1\)
nếu thấy đúng thì k cho mh nha
HA
30 tháng 4 2016
\(\frac{x+1}{5}+\frac{x+1}{6}=\frac{x+1}{7}+\frac{x+1}{8}\)
\(\Rightarrow\frac{x+1}{5}+\frac{x+1}{6}-\frac{x+1}{7}-\frac{x+1}{8}=0\)
\(\Rightarrow\left(x+1\right)\cdot\left(\frac{1}{5}+\frac{1}{6}-\frac{1}{7}-\frac{1}{8}\right)=0\)
\(\Leftrightarrow x+1=0\)
\(\Leftrightarrow x=-1\)
k nha
21 tháng 2 2018
\(\frac{1+0,6-\frac{3}{7}}{\frac{8}{3}+\frac{8}{5}-\frac{8}{7}}=\frac{\frac{3}{3}+\frac{3}{5}-\frac{3}{7}}{\frac{8}{3}+\frac{8}{5}-\frac{8}{7}}=\frac{3.\left(\frac{1}{3}+\frac{1}{5}-\frac{1}{7}\right)}{8.\left(\frac{1}{3}+\frac{1}{5}-\frac{1}{7}\right)}=\frac{3.1}{8.1}=\frac{3}{8}\)
\(\frac{\frac{1}{3}+0,25-\frac{1}{5}+0,125}{\frac{7}{6}+\frac{7}{8}-0,7+\frac{7}{16}}=\frac{\frac{1}{3}+\frac{1}{4}-\frac{1}{5}+\frac{1}{8}}{\frac{7}{6}+\frac{7}{8}-\frac{7}{10}+\frac{7}{16}}=\frac{1.\left(\frac{1}{3}+\frac{1}{4}-\frac{1}{5}+\frac{1}{8}\right)}{7.\left(\frac{1}{3}+\frac{1}{4}-\frac{1}{5}+\frac{1}{8}\right)}=\frac{1.1}{7.1}=\frac{1}{7}\)
=>\(\frac{3}{8}-\frac{1}{7}=\frac{13}{56}\)
SN
4 tháng 7 2016
a/ \(\frac{6}{7}x=\frac{18}{23}\)
\(x=\frac{18}{23}:\frac{6}{7}=\frac{21}{23}\)
b/ \(2\frac{1}{2}x=\frac{5}{6}\)
\(=>\frac{5}{2}x=\frac{5}{6}\)
\(x=\frac{5}{6}:\frac{5}{2}=\frac{1}{3}\)
c/\(x:2\frac{3}{4}=9\frac{5}{8}\)
\(x:\frac{11}{4}=\frac{77}{8}\)
\(x=\frac{77}{8}\cdot\frac{11}{4}=\frac{847}{32}\)
d/\(7\frac{1}{7}\cdot\frac{1}{7}\cdot x=22\frac{1}{8}\)
\(\frac{50}{49}x=\frac{177}{8}\)
\(x=\frac{177}{8}:\frac{50}{49}=\frac{8673}{400}\)
4 tháng 7 2016
\(a,\frac{6}{7}.x=\frac{18}{23}\) \(\Rightarrow x=\frac{18}{23}:\frac{6}{7}=\frac{18}{23}.\frac{7}{6}=\frac{21}{23}\)
\(b,2\frac{1}{2}.x=\frac{5}{6}\Rightarrow\frac{5}{2}.x=\frac{5}{6}\Rightarrow x=\frac{5}{6}:\frac{5}{2}=\frac{5}{6}.\frac{2}{5}=\frac{1}{3}\)
\(c,x:2\frac{3}{4}=9\frac{5}{8}\Rightarrow x:\frac{11}{4}=\frac{77}{8}\Rightarrow x=\frac{77}{8}.\frac{11}{4}=\frac{847}{32}\)
\(d,7\frac{1}{7}.\frac{1}{7}.x=22\frac{1}{8}\Rightarrow\frac{50}{49}.x=\frac{177}{8}\Rightarrow x=\frac{177}{8}:\frac{50}{49}=\frac{177}{8}.\frac{49}{50}=\frac{8673}{400}\)
NT
3
15 tháng 7 2017
\(\frac{x+1}{9}+\frac{x+2}{8}+\frac{x+3}{7}+...+\frac{x+9}{1}=-9\)
\(\left(\frac{x+1}{9}+1\right)+\left(\frac{x+2}{8}+1\right)+\left(\frac{x+3}{7}+1\right)+...+\left(\frac{x+9}{1}+1\right)=0\)
\(\frac{x+10}{9}+\frac{x+10}{8}+\frac{x+10}{7}+...+\frac{x+10}{1}=0\)
\(\left(x+10\right).\left(\frac{1}{9}+\frac{1}{8}+\frac{1}{7}+...+1\right)=0\)
vì \(\frac{1}{9}+\frac{1}{8}+\frac{1}{7}+...+1\ne0\)
\(\Rightarrow x+10=0\)
\(\Rightarrow x=-10\)
\(\frac{7}{x-1}=\frac{x+1}{8}\)
=> \(\left(x-1\right)\left(x+1\right)=56\)
=> \(x^2-1=56\)
=> \(x^2=57\)
=>\(\left[\begin{array}{nghiempt}x=\sqrt{57}\\x=-\sqrt{57}\end{array}\right.\)
thanks!