【紧急求助】已知（x的二分之一次方）+（x的负二分之一次方）=3,求…… ————要有解析过程,

x^(1/2）+x^(-1/2）=3,即：根号x+1/根号x=3x+1/x+2=9x+1/x=7[x^2-x^(-2)]÷[x^(3/2)-x^(-3/2)]=[(x+1/x)(x-1/x)]/[(根号x)^3-(1/根号x)^3]=[7*(x-1/x)]/[(根号x-1/根号x)(x+1+1/x)]=7(x-1/x)/[(根号x-1/根号x)(x+1/x+1)]=[7(根号x+1/根号x)(根号x-1/根号x)]/[(根号x-1/根号x)(7+1)]=7(根号x+1/根号x)/8=21/8 【问题补充：题中的两个“减去”都改为“加”】x^(1/2）+x^(-1/2）=3,即：根号x+1/根号x=3x+1/x+2=9x+1/x=7x^2+1/x^2+2=49x^2+1/x^2=47[x^2+x^(-2)]÷[x^(3/2)+x^(-3/2)]=(x^2+1/x^2)÷[(根号x)^3+(1/根号x)^3]=47/[(根号x+1/根号x)(x+1/x-1)]=47/[3*(7-1)]=47/18