先计算指数部分:1/2log7#14-1/2=1/2log7#(2*7)-1/2=1/2[log7#2+log7#7]-1/2=1/2log7#2+1/2-1/2=1/2log7#2(√7)^(1/2log7#2)=7^(1/2*1/2log7#2)=7^[log7#2^(1/4)]=2^1/4(2的1/4次方)
