\(A=x^{2005}-2005x^{2004}-x^{2004}+2005x^{2003}+x^{2003}-2005x^{2002}-.....+x^3-2005x^2-x^2+2005x+x-2005+2004\)\(=\left(x-2005\right)x^{2004}-\left(x-2005\right)x^{2003}+\left(x-2005\right)x^{2002}-....+\left(x-2005\right)x^2-\left(x-2005\right)x+\left(x-2005\right)+2004\)\(=\left(x-2005\right)\left(x^{2004}-x^{2003}+x^{2002}-......+x^2-x+1\right)+2004\)
Với x = 2005 => x - 2005 =0
=> A =2004
sao ma 2006.x2004 lai = 2005x2004 - x2004 duoc
nham y minh la sao 2006.x2004 = 2005x2004 - x2004 duoc minh tuong phai la 2006.x2004 = 2005x2004 nhan voi x2004 chu
