x+1/x=3 两平方得 x^2+1/x^2+1=9 得 x^2+1/x^2=8(x-1/x)^2=x^2+1/x^2-1=8-1=7所以 x-1/x= 7或-7(2)周长=2(a+b)=16 a+b=8 a-b-a^2+2ab-b^2+2=0 (a^2-2ab+b^2)-(a-b)-2=0 (a-b)^2-(a-b)-2=0 (a-b-2)(a-b+1)=0 a-b=2或a...