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13/15 - (13/21 + x) . 7/12 = 7/10
=> (13/21 + x). 7/12 = 13/15 - 7/10
=> (13/21 + x) . 7/12 = 1/6
=> 13/21 + x = 1/6 : 7/12
=> 13/21 + x = 2/7
=> x = 2/7 - 13/21
=> x = -1/3
\(a,\dfrac{2}{3}.x=\dfrac{2}{7}\\ x=\dfrac{2}{7}:\dfrac{2}{3}=\dfrac{3}{7}\\ ---\\ b,x.\dfrac{3}{5}=\dfrac{2}{5}\\ x=\dfrac{2}{5}:\dfrac{3}{5}=\dfrac{2}{3}\\ ---\\ c,x:\dfrac{8}{13}=\dfrac{13}{7}\\x=\dfrac{13}{7}.\dfrac{8}{13}=\dfrac{8}{7}\\ ----\\ d,\dfrac{3}{2}:x=\dfrac{7}{4}\\ x=\dfrac{3}{2}:\dfrac{7}{4}=\dfrac{3}{2}.\dfrac{4}{7}=\dfrac{6}{7}\)
\(|x-4|-13\)
\(\Leftrightarrow \left[\begin{array}{} x-4=13\\ x-4=-13 \end{array} \right.\)
\(\Leftrightarrow \left[\begin{array}{} x=13+4\\ x=(-13)+4 \end{array} \right.\)
\(\Leftrightarrow \left[\begin{array}{} x=17\\ x=-9 \end{array} \right.\)
Vậy x ∈ {17;-9}
\(4-\left(7-x\right)=x-\left(13-4\right)\)
\(4-7+x=x-13+4\)
\(x-x=-13+4-4+7\)
\(0x=-6\)(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 #
Lời giải:
$4-(7-x)=x(13-4)$
$4-7+x=x.9$
$-3+x=9x$
$-3=8x$
$x=\frac{-3}{8}$
\(đk:x\ne0;x\ne-1\\ \dfrac{3}{x}+\dfrac{x}{x+1}+\dfrac{x-3}{x}=\dfrac{13}{7}\\ \Leftrightarrow\dfrac{7.3.\left(x+1\right)}{7x\left(x+1\right)}+\dfrac{x.x.7}{7x\left(x+1\right)}+\dfrac{\left(x-3\right)\left(x+1\right).7}{7x\left(x+1\right)}=\dfrac{13.x.\left(x+1\right)}{7x\left(x+1\right)}\\ \Leftrightarrow\dfrac{21x+21+7x^2+7x^2+7x-21x-21}{7x\left(x+1\right)}=\dfrac{13x^2+13x}{7x\left(x+1\right)}\\ \Leftrightarrow14x^2+7x=13x^2+13x\\ \Leftrightarrow14x^2-13x^2=13x-7x\\ \Leftrightarrow x^2=6x\\ \Leftrightarrow x^2-6x=0\\ \Leftrightarrow x\left(x-6\right)=0\\ \Rightarrow\left[{}\begin{matrix}x=0\\x-6=0\end{matrix}\right.\\ \Rightarrow\left[{}\begin{matrix}x=0\left(kot/m\right)\\x=6\left(t/m\right)\end{matrix}\right.\Rightarrow x=6\)
x=-6 em nhé ;)
-x+7=13
=>-x=13-7
=>-x=6
=>x=-6