若n是奇数,则2的2n次方×(2的2n+1次方-1)的末两位数是要详细过程,无过程无分,过程详细正确加分
问题描述:
若n是奇数,则2的2n次方×(2的2n+1次方-1)的末两位数是
要详细过程,无过程无分,过程详细正确加分
答
28
令n=2k+1,则
2^(2n)·[2^(2n+1)-1]=2^[2(2k+1)]·{2^[2(2k+1)+1]-1}=2^(4k+2)·[2^(4k+3)-1]
=2·[2^(4k+2)]^2-2^(4k+2)
=2·[4·(2^4)^k]^2-4·(2^4)^k
=32·(16^k)^2-4·16^k
(100m+n)t=mt·100+nt,末两位为nt
(100m+n)^2=m^2·10000+2mn·100+n^2,末两位为n^2
考察末两位:
16^1=16,16^2=56,32·56-4·16=28
16^2=56,56^2=36,32·36-4·56=28
16^3=96,96^2=16,32·16-4·96=28
16^4=36,36^2=96,32·96-4·36=28
16^5=76,76^2=76,32·76-4·76=28
16^6=16,……
……
注:x^y表示x的y次方.