2. a, Ư(24)={1,2,3,4,6,8,...}
Ư(40)={1,2,4,5,8,...} =>ƯCLN(24,40)={8}
b, B(2)={0,2,4,6,8,10,...}
B(8)={0,8,16,...} =>BCNN(2,8)={8}
c, Ư(20)={1,2,4,5,10,..}
Ư(30)={1,3,5,6,10,..} =>ƯCLN(20,30)={10}
d, B(10)={0,10,20,30,..,}
B(15)={0,15,30,....} =>BCNN(10,15)={30}