Tìm ƯCLN (120, 78, 168)
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a) Ta có:
144=24.3
420=22.3.5.7
ƯCLN(...)=22.3=12
ƯC(...)=Ư(12)={1;2;3;4;6;12}
Các bài sau bn cũng lm thế này nhé:)))
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a) 54=2.33; 48=23.6 b)45=5.32 ; 60=22.3.5 c)48=24.3 ; 72=22.32 ;90=2.32.5
TSNT chung:2 TSNT chung:3;5 TSNT chung:2;3
ƯCLN(54;48)=2=2 ƯCLN(45;60)=3.5=15 ƯCLN(48;72;90)=2.3=6
ƯC(54;48)=Ư(2)={1;2} ƯC(45;60)=Ư(15)={1;3;5;15} ƯC(48;72;60)=Ư(6)={1;2;3;6}
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Đáp án: A
Tìm ƯCLN (48; 168; 360)
48 = 24.3
168 = 23.3.7
360 = 23.32.5
ƯCLN (48; 168; 360) = 23.3 = 24
A. 24
B. 45
C. 168
D. 40
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Lời giải:
$100=2^2.5^2$
$120=2^3.3.5$
$\Rightarrow ƯCLN(100,120)=2^2.5=20$
![](https://rs.olm.vn/images/avt/0.png?1311)
Câu 1
a) \(48=2^4.3\)
\(60=2^2.3.5\)
\(72=2^3.3^2\)
\(ƯCLN\left(48;60;72\right)=2^2.3=12\)
\(ƯC\left(48;60;72\right)=Ư\left(12\right)=\left\{1;2;3;4;6;12\right\}\)
b) \(42=2.3.7\)
\(55=5.11\)
\(91=7.13\)
\(ƯCLN\left(42;55;91\right)=1\)
\(ƯC\left(42;55;91\right)=\left\{1\right\}\)
c) \(48=2^4.3\)
\(72=2^3.3^2\)
\(ƯCLN\left(48;72\right)=2^3.3=24\)
\(ƯC\left(48;72\right)=Ư\left(24\right)=\left\{1;2;3;4;6;8;12;24\right\}\)
Câu 2:
120 ⋮ \(x\); 168 ⋮ \(x\); 216 ⋮ \(x\);
\(x\) \(\in\) ƯC(120; 168; 216)
120 = 23.3.5; 168 = 23.3.7; 216 = 23.33
ƯClN(120; 168; 216) = 23.3 = 24
\(x\) \(\in\) Ư(24) = {1; 2; 3; 4; 6; 8; 12; 24}
Vì \(x\) > 20 nên \(x\) = 24
Ta có: 120 = 2^3 x 3 x 5
78 = 2 x 3 x 13
168 = 2^3 x 3 x 7
=> ƯCLN(120;78;168) = 2 x 3 = 6