1)
_13.[a-1]-4=_44.(2^4-15)+(-2011)^0
_13.[a-1]-4=_43
_13.[a-1] =_43+4
_13.[a-1] =_39
[a-1] =_39:13
[a-1] =3
TH1. TH2
a-1=3. a-1=_3
a. =3+1. a. =_3-1
a. =4. a. =-4
a∈{4;_4}
2)
A=2010.2010^1.2010^2… .2010^2009.2010^2010
=2010.(2010+2010^2)….2010^2006.(2010+2010^2+2010^3)
=2010.8124643110…2010^2006.tự tính chia hết cho 2011