a) Ta có :60 = 23 . 3 . 5; 280 = 22 . 5 .7
⇒BCNN(60,280) = 23 . 3 . 5 . 7 = 840
⇒BC(60,280)=B(840)={0;840;1680;2520;....}
b) Ta có 84 = 22 . 3 . 7;108 = 22 . 33
⇒BCNN(84,108) = 22 . 33 . 7 = 756.
⇒BC(84,108) =B(756)={0;756;1512;2268;...}
c) 13 = 13;15 = 3 . 5
⇒BCNN(13, 15) = 3 . 5 . 13 = 195.
⇒BC(13, 15) =B(195)={0;195;390;585;...}
d)Ta có :10 = 2.5; 12 = 22.3; 15 = 3.5
⇒ BCNN(10, 12, 15) = 22.3.5 = 60.
⇒BCN(0, 12, 15) =B(60)={0;60;120;180;..}