d^2=(x-a)^2+y^2=x^2-2ax+a^2+1-(x^2)/2=(x^2)/2-2ax+a^2+1=(1/2)*(x-2a)^2+1-a^2由于x的取值范围是[-√2,√2],因此要分类讨论了：当2a∈[-√2,√2]即a∈[-√2/2,√2/2]时,d^2有最小值1-a^2当|2a|>√2时,.省略,PLS.D...