Tìm x, biết: 1/2+1/3+1/12+1/18+1/x=1
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Ta có: 1/2+1/3+1/12+1/18 =18/36+12/36+3/36+2/36=35/36. Vậy 35/36+1/x=1 => x=36
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1.8100
2. 34 x 18 + 18 x 66
= 18 x ( 34 + 66)
= 18 x 100 = 1800
3. X × ( 8 + 12) = 160 + 20 × 12
= X x 20 = 160 + 240
= X x 20 = 400
X = 400 : 20 = 20
4. X x 12 - X x 2 = 2020
(12 - 2) x X = 2020
10 x X = 2020
X = 2020 : 10 = 202
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a: =>-12<x<2y<-9
=>x=-11; y=-5
b: =>-7<3(x-1)<8
\(\Leftrightarrow3\left(x-1\right)\in\left\{-6;-3;0;3;6\right\}\)
\(\Leftrightarrow x-1\in\left\{2;1;0;-1;-2\right\}\)
hay \(x\in\left\{3;2;1;0;-1\right\}\)
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1: =>x/5=6/5
=>x=6
2: =>x^2=36
=>x=6 hoặc x=-6
3: =>x-5/2=3+1/6=19/6
=>x=19/6+5/2=19/6+15/6=34/6=17/3
4: =>x=1/2:2/5=1/2*5/2=5/4
![](https://rs.olm.vn/images/avt/0.png?1311)
a.-1,75-(-\(\dfrac{1}{9}\)-2\(\dfrac{1}{8}\))
-1,75-\(\dfrac{1}{9}+\dfrac{17}{8}\)
\(-\dfrac{7}{4}-\dfrac{1}{9}+\dfrac{17}{8}\)
\(\dfrac{-126}{72}-\dfrac{8}{72}+\dfrac{153}{72}\)
=\(\dfrac{19}{72}\)
b.\(\dfrac{-1}{12}-\left(2\dfrac{5}{8}-\dfrac{1}{3}\right)\)
\(\dfrac{-1}{12}-\left(\dfrac{21}{8}-\dfrac{1}{3}\right)\)
\(\dfrac{-1}{12}-\dfrac{21}{8}+\dfrac{1}{3}\)
\(\dfrac{-2}{24}-\dfrac{63}{24}+\dfrac{64}{24}\)
=\(\dfrac{-1}{24}\)
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\(12\left(x-3\right)=5\left(x-1\right)+4\)
\(\Rightarrow12x-36=5x-5+4\)
\(\Rightarrow12x-5x=-5+4+36\)
\(\Rightarrow7x=35\)
\(\Rightarrow x=5\)
\(-6\left(x-7\right)+2\left(x+10\right)=x-18\)
\(-6x+42+2x+20=x-18\)
\(-6x+2x-x=-18-20-42\)
\(-5x=-80\)
\(x=16\)
\(7\left(2x-1\right)-12\left(x-5\right)=3\)
\(\Rightarrow14x-7-12x+60=3\)
\(\Rightarrow14x-12x=3-60+7\)
\(\Rightarrow2x=-50\)
\(\Rightarrow x=-25\)
\(\left|2x-1\right|=17\)
\(\Leftrightarrow\orbr{\begin{cases}2x-1=17\\2x-1=-17\end{cases}}\)
\(\Leftrightarrow\orbr{\begin{cases}x=9\\x=-8\end{cases}}\)
\(\left|8-3x\right|=14\)
\(\Leftrightarrow\orbr{\begin{cases}8-3x=14\\8-3x=-14\end{cases}}\)
\(\Leftrightarrow\orbr{\begin{cases}x=-2\\x=\frac{22}{3}\end{cases}}\)
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\(\left(\dfrac{103}{8}-\dfrac{193}{18}\right):x-\dfrac{40}{33}:\dfrac{8}{11}=\dfrac{5}{3}\)
\(\dfrac{155}{72}:x-\dfrac{5}{3}=\dfrac{5}{3}\)
\(\dfrac{155}{72}:x=\dfrac{5}{3}+\dfrac{5}{3}=\dfrac{10}{3}\)
\(x=\dfrac{155}{72}:\dfrac{10}{3}=\dfrac{31}{48}\)
vaayj.....
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1) Do x ∈ Z và 0 < x < 3
⇒ x ∈ {1; 2}
2) Do x ∈ Z và 0 < x ≤ 3
⇒ x ∈ {1; 2; 3}
3) Do x ∈ Z và -1 < x ≤ 4
⇒ x ∈ {0; 1; 2; 3; 4}
Ta có: 1/2+1/3+1/12+1/18 =18/36+12/36+3/36+2/36=35/36. Vậy 35/36+1/x=1 => x=36