解：x+1/x=3左右两边同时平方 x²+1+1/x²=9∴x²+1/x²=8（x-1/x）²=x²-1+1/x²=8-1=72、x²-2xy-(x²／3y²)+xy×(3y-x)/(x-y)+(1/x+1/y)÷(1/x-1/y) 是不是3(y-x)呀解：原式=x²-2xy-(x²／3y²)-xy×(3y-x)/(x-y)+(1/x+1/y)÷(1/x-1/y)
