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\(\frac{x-7}{36}=-\frac{4}{7-x}\)
\(\frac{x-7}{36}=\frac{4}{x-7}\)
\(\Rightarrow\left(x-7\right)^2=36.4=144\)
\(\left(x-7\right)^2=12^2\)
\(\Rightarrow\orbr{\begin{cases}x-7=12\Rightarrow x=12+7=19\\x-7=-12\Rightarrow x=-12+7=-5\end{cases}}\)
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a)\(\frac{2}{42}+\frac{2}{56}+...+\frac{2}{x\left(x+2\right)}=\frac{2}{9}\)
\(2\left(\frac{1}{6.7}+\frac{1}{7.8}+...+\frac{1}{x\left(x+2\right)}\right)=\frac{2}{9}\)
\(2\left(\frac{1}{6}-\frac{1}{7}+\frac{1}{7}-\frac{1}{8}+...+\frac{1}{x}-\frac{1}{x+2}\right)=\frac{2}{9}\)
\(\frac{1}{6}-\frac{1}{x+2}=\frac{2}{9}:2\)
\(\frac{1}{x+2}=\frac{1}{6}-\frac{1}{9}\)
\(\frac{1}{x+2}=\frac{1}{18}\)
=>x+2=18
=>x=16
b tương tự nhân nó với 1/2
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Ta có : \(\frac{7}{x-2005}+\frac{4}{5.9}+\frac{4}{9.13}+...+\frac{4}{41.45}=\frac{29}{45}\)
\(\Rightarrow\frac{7}{x-2005}=\frac{29}{45}-\left(\frac{4}{5.9}+\frac{4}{9.13}+...+\frac{4}{41.45}\right)\)
\(\Rightarrow\frac{7}{x-2005}=\frac{29}{45}-\left(\frac{1}{5}-\frac{1}{9}+\frac{1}{9}-\frac{1}{13}+...+\frac{1}{41}-\frac{1}{45}\right)\)
\(\Rightarrow\frac{7}{x-2005}=\frac{29}{45}-\left(\frac{1}{5}-\frac{1}{45}\right)=\frac{29}{45}-\frac{8}{45}=\frac{7}{15}\)
\(\Rightarrow x-2005=15\Rightarrow x=15+2005=2020\)
Vậy x =2020
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\(\frac{4}{7}\times x=\frac{1}{5}+\frac{2}{3}\)
\(\frac{4}{7}x=\frac{13}{15}\)
\(\Rightarrow x=\frac{91}{60}\)
các bài còn lại tương tự nha
mấy cái này dễ mà toán tìm x này là cơ bản!!
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\(\frac{3}{2}-\frac{2}{7}< \frac{2}{3}x+\frac{3}{4}< \frac{1}{2}\)\(+\frac{7}{9}\)
=\(\frac{17}{14}< \frac{2}{3}x+\frac{3}{4}< \frac{23}{18}\)
=\(\frac{17}{14}-\frac{3}{4}< \frac{2}{3}x+\frac{3}{4}< \frac{23}{18}-\frac{3}{4}\)
=\(\frac{13}{28}< \frac{2}{3}x< \frac{19}{36}\)
=\(\frac{117}{252}< \frac{2}{3}x< \frac{133}{252}\)
=
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Bài làm:
Pt <=> \(\left(\frac{x-1}{2020}-1\right)+\left(\frac{x-3}{2018}-1\right)+\left(\frac{x-5}{2016}-1\right)+\left(\frac{x-7}{2014}-1\right)=4-4\)
\(\Leftrightarrow\frac{x-2021}{2020}+\frac{x-2021}{2018}+\frac{x-2021}{2016}+\frac{x-2021}{2014}=0\)
\(\Rightarrow x-2021=0\Rightarrow x=2021\)
(x-7)/36=4/(x-7)
=> (x-7)2 = 4x36=144
=> x-7 =12 hoặc -x+7 = 12
=> x=19 hoặc x = -5
\(\Leftrightarrow\)(x-7)(7-x)=-144
\(\Leftrightarrow\)-\(x^2\)+14x - 49 = - 144
\(\Leftrightarrow\)-x\(^2\)+ 14x + 95 = 0
\(\Leftrightarrow\)\(\orbr{\begin{cases}x=-5\\x=19\end{cases}}\)