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a: \(\Leftrightarrow\left(x;y-3\right)\in\left\{\left(1;17\right);\left(17;1\right);\left(-1;-17\right);\left(-17;-1\right)\right\}\)
=>\(\left(x,y\right)\in\left\{\left(1;20\right);\left(17;4\right);\left(-1;-14\right);\left(-17;2\right)\right\}\)
b: \(\Leftrightarrow\left(x-1;y+2\right)\in\left\{\left(1;7\right);\left(7;1\right);\left(-1;-7\right);\left(-7;-1\right)\right\}\)
=>\(\left(x,y\right)\in\left\{\left(2;5\right);\left(8;-1\right);\left(0;-9\right);\left(-6;-3\right)\right\}\)
c: =>(y+1)(3x+1)=7
=>\(\left(3x+1;y+1\right)\in\left\{\left(1;7\right);\left(7;1\right)\right\}\)
=>\(\left(x,y\right)\in\left\{\left(0;6\right);\left(2;0\right)\right\}\)
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280 chia hết cho x ; 700 chia hết cho x ; 420 chia hết cho x và 40 < x < 100
=> x ∈ ƯC( 280 ; 700 ; 420 ) và 40 < x < 100
280 = 23 . 5 . 7
700 = 22 . 52 . 7
420 = 22 . 3 . 5 . 7
=> ƯCLN( 280 ; 700 ; 420 ) = 22 . 5 . 7 = 140
=> ƯC( 280 ; 700 ; 420 ) = Ư(140) = { 1 ; 2 ; 4 ; 5 ; 7 ; 10 ; 14 ; 20 ; 28 ; 35 ; 70 ; 140 }
mà 40 < x < 100
=> x = 70
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ƯCLN (90; 150) = 30. Mà Ư (30) = {1; 2; 3; 5; 6; 10; 15; 30}.
Vì 5< x < 30 nên x ϵ{6; 10; 15;30}.
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a: 2x+16=30
=>2x=30-16=14
=>x=14/2=7
b: \(2\left(x+1\right)^3+5=59\)
=>\(2\left(x+1\right)^3=54\)
=>\(\left(x+1\right)^3=27\)
=>x+1=3
=>x=2
c: \(x\inƯ\left(24\right)\)
=>\(x\in\left\{1;2;3;4;6;8;12;24\right\}\)
mà 2<=x<=12
nên \(x\in\left\{2;3;4;6;8;12\right\}\)
d: \(x-2⋮5\)
=>\(x-2\in\left\{0;5;10;15;20;25;30;35;...\right\}\)
=>\(x\in\left\{2;7;12;17;22;27;32;...\right\}\)
mà x<=30
nên \(x\in\left\{2;7;12;17;22;27\right\}\)
a) 2.x + 16 = 30
2x = 30 - 16
2x = 14
x = 14 : 2
x = 7
b) 2.(x + 1)³ + 5 = 59
2.(x + 1)³ = 59 - 5
2.(x + 1)³ = 54
(x + 1)³ = 54 : 2
(x + 1)³ = 27
(x + 1)³ = 3³
x + 1 = 3
x = 3 - 1
x = 2
c) x ∈ Ư(20) = {1; 2; 4; 5; 10; 20}
Mà 2 ≤ x ≤ 12
⇒ x ∈ {2; 4; 5; 10}
d) (x - 2) ⋮ 5 nên x - 2 ∈ B(5) = {0; 5; 10; 15; 20; 25; 30; 35; ...}
x {2; 7; 12; 17; 22; 27; 32; 37; ...}
Mà x ≤ 30
⇒ x ∈ {2; 7; 12; 17; 22; 27}
![](https://rs.olm.vn/images/avt/0.png?1311)
Đáp án cần chọn là: B
+) Vì 90⋮x nên x∈ Ư(90) = {1;2;3;5;6;9;15;18;10;30;45;90}
+) Vì 150⋮x nên x∈ Ư(150)={1;2;3;5;6;10;15;25;30;50;75;150}
Nên x∈ ƯC(90;120)={1;2;3;5;6;10;15;30} mà 5<x<30 nên x∈{6;10;15}
![](https://rs.olm.vn/images/avt/0.png?1311)
\(a.-7< x< -1\\ x\in\left\{-6;-5;-4;-3;-2\right\}\\ \Rightarrow\left(-6\right)+\left(-5\right)+\left(-4\right)+\left(-3\right)+\left(-2\right)\\ =-20\)
\(b.-1\le x\le6\\ x\in\left\{-1;0;1;2;3;4;5;6\right\}\\ \Rightarrow\left(-1\right)+0+1+2+3+4+5+6\\ =20\)
\(c.-5\le x< 6\\ x\in\left\{-5;-4;-3;-2;-1;0;1;2;3;4;5\right\}\\ \Rightarrow-5-4+-3+-2+-1+0+1+2+3+4+5\\ =0\)
![](https://rs.olm.vn/images/avt/0.png?1311)
Bài 3:
a: Ta có: 60-3(x-2)=51
\(\Leftrightarrow x-2=3\)
hay x=5
b: Ta có: \(4x-20=25:2^2\)
\(\Leftrightarrow4x=\dfrac{25}{4}+20=\dfrac{105}{4}\)
hay \(x=\dfrac{105}{16}\)
c: Ta có: \(8\cdot6+288:\left(x-3\right)^2=50\)
\(\Leftrightarrow288:\left(x-3\right)^2=50-48=2\)
\(\Leftrightarrow\left(x-3\right)^2=144\)
\(\Leftrightarrow\left[{}\begin{matrix}x-3=12\\x-3=-12\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=15\\x=-9\end{matrix}\right.\)
a) 15
b) câu 2 chép đề liều
Khang Kavin câu b sao hử