令2^(1/2)x=a
则2^x=a^2
a^2+a-42=0
(a+7)(a-6)=0
因为2^(1/2)x 〉0
所以a+7=0不成立
a=6
2^(1/2)x=6
(1/2)x=log(2)6
x=2log(2)6=log(2)36