(1/2)^a+(1/4)^b+(1/8)^c=(1/2)^a+(1/2)^2b+(1/2)^3c≥3[(1/2)^a•(1/2)^2b•(1/2)^3c]^(1/3)=3[(1/2)^(a+2b+3c)]^(1/3)=3(1/2)^(1/2)=3√2/2即最小值为3√2/2
