设t=2^(1/8),则2^(1/4)=t^2, 2^(1/2)=t^4, t^8=2
(1+(2^(-1/8)))*(1+(2^(-1/4)))*(1+(2^(-1/2)))
=(1+1/2^(1/8))*(1+1/2^(1/4))*(1+1/2(1/2))
=(1+1/t)(1+1/t^2)(1+1/t^4)
=(t+1)(t^2+1)(t^4+1)/t^7
=(t^7+t^6+t^5+t^4+t^3+t^2+t+1)/t^7
=(t^8-1)/(t^7*(t-1))
=(t^8-1)/(t^8-t^7)
=(2-1)/(2-2^(7/8))
=1/(2-(2^(7/8))
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