goi so can tim la abc.

theo de bai ta co b2=a.c

abc-cba=495

=>a.100+b.10+c-c.100+b.10.a=495

=>(a.100-a)-(b.10-b.10)-(c.100 -c)=495

=>99.a-99.c=495

=>99.(a-c)

=>a-c=5

=>c=a-5

vi a<10=>a-5<5=>0<c<5

=>c=1,2,3,4

xet c=1 =>1+5=6

=>b2=1.6=6=>loai

xet c=2=>2+5=7

=>b2=2.7=14=>loai

xet c=3=>3+5=8

=>b2=3.8=24=>loai

xetc=4=>4=5=9

=>b2=4.9=36=>36=62 chon

=>b=6=>abc=964

so can tim la 964