ta có : \(B=2004+2004^2+2004^3+...+2004^{10}\)
\(B=\left(2004+2004^2\right)+\left(2004^3+2004^4\right)+...+\left(2004^9+2004^{10}\right)\)
\(B=2004.\left(1+2004\right)+2004^3\left(1+2004\right)+...+2004^9\left(1+2004\right)\)
\(B=2004.2005+2004^3.2005+...+2004^9.2005\)
\(B=2005.\left(2004+2004^3+...+2004^9\right)⋮2005\)
\(\Rightarrow2005.\left(2004+2004^3+2004^9\right)\) chia hết cho \(2005\)
\(\Leftrightarrow B=2004+2004^2+2004^3+...+2004^{10}\) chia hết cho \(2005\) (đpcm)
B=2004 + 20042 + 20043 + ... + 200410
B=(2004 + 20042) + (20043 + 20044) + ... + (20049 + 200410)
B=2004.(1 + 2004) + 20043(1 + 2004) + ... + 20049(1 + 2004)
B=2004.2005 + 20043.2005 + ... + 20049.2005
B=2005.(2004 + 20043 + ... + 20049) ⋮ 2005 (đpcm)
