b,B=(2+1)(2^2+1)(2^4+1)(2^8+1)B=(2+1)(2^2+1)(2^4+1)(2^8+1)
=(2−1)(2+1)(2^2+1)(2^4+1)(2^8+1)=(2−1)(2+1)(2^2+1)(2^4+1)(2^8+1)
=(2^2−1)(2^2+1)(2^4+1)(2^8+1)=(2^2−1)(2^2+1)(2^4+1)(2^8+1)
=(2^4−1)(2^4+1)(2^8+1)=(2^4−1)(2^4+1)(2^8+1)
=(2^8−1)(2^8+1)=(2^8−1)(2^8+1)
=21^6−1=21^6−1
Vì 21^6>21^6−1 nên A>B
c,A = 2011 . 2013=(2012-1).(2012+1)=2012^2-1<2012^2
<=>A<B