A = { x E N | 18 < x < 21}
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![](https://rs.olm.vn/images/avt/0.png?1311)
![](https://rs.olm.vn/images/avt/0.png?1311)
A = { 19 ; 20 }
B = { 1 ; 2 ; 3 }
C = { 35 ; 36 ; 37 ; 38 }
![](https://rs.olm.vn/images/avt/0.png?1311)
A = { 19;20 }
B = { 1;2;3 }
C = { 35;36;37;38 } k cho mik với nhé bn
![](https://rs.olm.vn/images/avt/0.png?1311)
A. 3x(x-1) = 21
x-1 = 21: 3
x-1 = 7
x = 7+1
x = 8
Vậy x=8
B. 30-3x(x-2)=18
3x(x-2)= 30-18
3x(x-2)= 12
x-2 = 12:3
x-2 = 4
x = 4+2
x = 6
Vậy x=6
\(a,3\left(x-1\right)=21\)
\(3x-3=21\)
\(3x=21+3\)
\(3x=24\)
\(x=8\)
\(b,30-3\left(x-2\right)=18\)
\(30-3x+6=18\)
\(30-3x=18-6\)
\(30-3x=12\)
\(3x=30-12\)
\(3x=18\)
\(x=6\)
![](https://rs.olm.vn/images/avt/0.png?1311)
a) D = { 19 ; 20 }
b) E = { 1 ; 2 ; 3 }
c) Thiếu đề bài
d) D = { 16 ; 17 ; 18 ; 19 ; 20 }
![](https://rs.olm.vn/images/avt/0.png?1311)
\(A=\left\{19;20\right\}\)
\(B=\left\{1;2;3;\right\}\)
\(C=\left\{35;36;37;38\right\}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
\(a) x\in Ư(18)\) và \(x \in B(3)\)
\(Ư(18)=\){ 1;2;3;6;9;18}
\(B(3) = \){0;3;6;9;12;15;18}
=> x \(\in\) {3;6;9;18}
\(b) x\in Ư(28)\) và \(x\in Ư(21)\)
=> x \(\in\) ƯC(28,21)
Ta có :
28 = 22.7
21 = 3,7
=> ƯCLN(28,21) = 7
ƯC(28,21) = Ư(7) = {1;7}
![](https://rs.olm.vn/images/avt/0.png?1311)
Bài 1:
a) \(\dfrac{4}{14}-x=\dfrac{10}{-21}\)
\(\Leftrightarrow x=\dfrac{4}{14}-\dfrac{10}{-21}\)
\(\Leftrightarrow x=\dfrac{16}{21}\)
Vậy ...
b) \(\dfrac{4}{14}:x=\dfrac{-21}{-20}\)
\(\Leftrightarrow\dfrac{4}{14.x}=\dfrac{21}{20}\)
\(\Leftrightarrow21.14.x=20.4\)
\(\Leftrightarrow294x=80\)
\(\Leftrightarrow x=\dfrac{40}{147}\)
Vậy ...
c) \(75\%.x+3=18\)
\(\Leftrightarrow\dfrac{3}{4}x=15\)
\(\Leftrightarrow x=20\)
Vậy ...
d) \(2x+1=32\)
\(\Leftrightarrow2x=31\)
\(\Leftrightarrow x=\dfrac{31}{2}\)
Vậy ...
Bài 1
A) \(\dfrac{4}{14}-x=\dfrac{10}{-21}\)
\(\Leftrightarrow x=\dfrac{4}{14}-\dfrac{10}{-21}\)
\(\Leftrightarrow x=\dfrac{4}{14}+\dfrac{10}{21}=\dfrac{12}{42}+\dfrac{20}{42}=\dfrac{32}{42}=\dfrac{16}{21}\)
B) \(\dfrac{4}{14}:x=\dfrac{-21}{-20}\)
\(\Leftrightarrow\dfrac{4}{14}.\dfrac{1}{x}=\dfrac{21}{20}\)
\(\Leftrightarrow\dfrac{4}{14x}=\dfrac{21}{20}\)
\(\Leftrightarrow20.4=21.14x\) (tích chéo)
\(\Leftrightarrow80=294x\)
\(\Leftrightarrow x=\dfrac{40}{147}\)
C) 75%.x + 3 = 18
\(\Leftrightarrow\dfrac{3}{4}x=15\)
\(\Leftrightarrow x=15:\dfrac{3}{4}=15.\dfrac{4}{3}=20\)
E) 2x + 1 = 32
<=> 2x = 31
<=> x = \(\dfrac{31}{2}\)
A = 19,20
A Thuoc { 19,20 }