急急急！高一数学必修一人教A版第60页习题2.1B组第二题

1.因为[(x^1/2)+(x^-1/2)]^2
=x+(x^-1)+2
=3+2
=5,
且(x^1/2)+(x^-1/2)>0,
所以(x^1/2)+(x^-1/2)=根号5；

2.因为[x+(x^-1)]^2
=(x^2)+(x^-2)+2
=3^2=9,
所以(x^2)+(x^-2)=7；

3.因为[x-(x^-1)]^2
=(x^2)+(x^-2)-2
=7-2=5,
所以x-(x^-1)=根号5或-根号5，
所以(x^2)-(x^-2)
=[x+(x^-1)][x-(x^-1)],
因为x+(x^-1)=3,x-(x^-1)=根号5或-根号5，
所以(x^2)+(x^-2)=3根号5或-3根号5.