? $ \underbrace {222…22}_{2000個(gè)2}×\underbrace {999…99}_{2000個(gè)9}$?
?$=\underbrace {222…22}_{2000個(gè)2}×(1\underbrace {000…00}_{2000個(gè)0}-1)$?
?$=\underbrace {222…22}_{2000個(gè)2}×1\underbrace {000…00}_{2000個(gè)0}-\underbrace {222…22}_{2000個(gè)2}$?
?$=\underbrace {222…22}_{1999個(gè)2}21\underbrace {777…78}_{1999個(gè)7}$?