（1）0.25^4*8^2
=(1/4)^4*2^6
=2^(-8)*2^6
=2^(-2)
=1/4
（2）（1/2）^8*8^6*0.25^5
=2^(-8)*2^18*(2^-2)^5
=2^10*2^(-10)
=2^0
=1