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a) Ta có :
12 = 22 x 3
18 = 2 x 32
=) BCNN ( 12; 18 ) = 22 x 32 = 36.
=) BC ( 12; 18 ) = B ( 36 ) = \(\left\{0;36;72;108;...\right\}\)
b) A = \(\left\{3;9;15;21;27\right\}\)
và 
và x < 500 b) 
và 
a: UCLN(16;42)=2
UC(16;42)={1;2}
b: UCLN(168;120;144)=24
UC(168;120;144)={1;2;3;4;6;8;12;24}
a: BCNN(105;120)=840
BC(105;120)={840;1680;...}
b: BCNN(192;440)=10560
BC(192;440)={10560;21120;...}
c: BCNN(252;792)=5544
d: BCNN(45;120;270)=1080
e: BCNN(128;192;320)=1920
f: BCNN(135;225;405)=2025
a: \(42=2\cdot3\cdot7;70=2\cdot5\cdot7\)
=>\(BCNN\left(42;70\right)=2\cdot3\cdot5\cdot7=210\)
=>\(BC\left(42;70\right)=B\left(210\right)=\left\{0;210;420;...\right\}\)
b: \(70=2\cdot5\cdot7;180=3^2\cdot5\cdot2^2\)
=>\(BCNN\left(70;180\right)=2^2\cdot3^2\cdot5\cdot7=1260\)
=>\(BC\left(70;180\right)=\left\{1260;2520;...\right\}\)
c: \(5=5;7=7;8=2^3\)
=>\(BCNN\left(5;7;8\right)=5\cdot7\cdot8=280\)
=>\(BC\left(5;7;8\right)=\left\{280;560;...\right\}\)
d: \(12=2^2\cdot3;18=3^2\cdot2\)
=>\(BCNN\left(12;18\right)=2^2\cdot3^2=36\)
=>\(BC\left(12;18\right)=\left\{36;72;...\right\}\)
e: \(15=3\cdot5;18=3^2\cdot2\)
=>\(BCNN\left(15;18\right)=3^2\cdot2\cdot5=90\)
=>\(BC\left(15;18\right)=\left\{90;180;...\right\}\)
f: \(84=2^2\cdot3\cdot7;108=3^3\cdot2^2\)
=>\(BCNN\left(84;108\right)=2^2\cdot3^3\cdot7=756\)
=>\(BC\left(84;108\right)=\left\{756;1512;...\right\}\)
j: \(33=3\cdot11;44=2^2\cdot11;55=5\cdot11\)
=>\(BCNN\left(33;44;55\right)=3\cdot2^2\cdot5\cdot11=660\)
=>\(BC\left(33;44;55\right)=\left\{660;1320;...\right\}\)
g: \(1=1;12=2^2\cdot3;27=3^3\)
=>\(BCNN\left(1;12;27\right)=1\cdot2^2\cdot3^3=108\)
=>\(BC\left(1;12;27\right)=\left\{108;216;...\right\}\)
n: \(5=5;9=3^2;11=11\)
=>\(BCNN\left(5;9;11\right)=5\cdot3^2\cdot11=495\)
=>\(BC\left(5;9;11\right)=\left\{495;990;...\right\}\)