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\(\dfrac{4-x}{-5}=\dfrac{-5}{4-x}\)
\(\Leftrightarrow\left(4-x\right)\left(4-x\right)=-5\times-5\)
\(\Rightarrow\left(4-x\right)^2=25\)
\(\Rightarrow\left[{}\begin{matrix}4-x=5\\4-x=-5\end{matrix}\right.\)
\(\Rightarrow\left[{}\begin{matrix}x=-1\\x=9\end{matrix}\right.\)
\(\dfrac{4-x}{-5}=\dfrac{-5}{4-x}\)
\(\Rightarrow\left(4-x\right).\left(4-x\right)=\left(-5\right).\left(-5\right)\)
\(\Rightarrow\left(4-x\right)^2=25\)
\(\Rightarrow\left(4-x\right)^2=5^2\)
\(\Rightarrow4-x=\pm5\)
\(\Rightarrow\left[{}\begin{matrix}4-x=5\\4-x=-5\end{matrix}\right.\)
\(\Rightarrow\left[{}\begin{matrix}x=4-5\\x=4-\left(-5\right)\end{matrix}\right.\)
\(\Rightarrow\left[{}\begin{matrix}x=-1\\x=9\end{matrix}\right.\)
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\(a,\dfrac{2}{3}.x=\dfrac{2}{7}\\ x=\dfrac{2}{7}:\dfrac{2}{3}=\dfrac{3}{7}\\ ---\\ b,x.\dfrac{3}{5}=\dfrac{2}{5}\\ x=\dfrac{2}{5}:\dfrac{3}{5}=\dfrac{2}{3}\\ ---\\ c,x:\dfrac{8}{13}=\dfrac{13}{7}\\x=\dfrac{13}{7}.\dfrac{8}{13}=\dfrac{8}{7}\\ ----\\ d,\dfrac{3}{2}:x=\dfrac{7}{4}\\ x=\dfrac{3}{2}:\dfrac{7}{4}=\dfrac{3}{2}.\dfrac{4}{7}=\dfrac{6}{7}\)
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\(4-\left(7-x\right)=x-\left(13-4\right)\)
\(4-7+x=x-13+4\)
\(x-x=-13+4-4+7\)
\(0x=-6\)(Vô lí)
Vậy không có giá trị x thỏa biểu thức
Bài làm
4 - ( 7 - x ) = x - ( 13 - 4 )
4 - 7 + x = x - 13 + 4
x - x = 7 - 4 - 13 + 4
x( 1 - 1 ) = -6
x . 0 = -6
0 = -6 ( Vô lí )
Vậy \(x\in\varnothing\)
# Học tốt #
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Lời giải:
$4-(7-x)=x(13-4)$
$4-7+x=x.9$
$-3+x=9x$
$-3=8x$
$x=\frac{-3}{8}$
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4 - ( 7 - x ) = x - ( 13 - 4 )
4 - ( 7 - x ) = x - 9
7 - x = x - 9 - 4 = x - 13
7 - x = x - 13
=> x = 10
4 - ( 7 - x ) = x - 9
4 - 7 + x = x - 9
-3 + x = x - 9
-3 + 9 = 2x
6 = 2x
3 = x
Vậy x = 3