x+1/x=3(1)x^2+1/x^2=(x+1/x)^2-2=9-2=7(2)(x-1/x)^2=x^2+1/x^2-2=7-2=5
x+1/x=3,求(1)x^2+1/x^2(2)(x-1/x)^2(1) x^2+ 1 /x^2=（x+ 1/x）^2 -2=3^2 -2=7(2) (x-1/x)^2 = （x+ 1/x）^2 - 4=3^2 -4=5
