f(x-1/x)=x²+1/x²=（x-1/x）²+2所以f(x）=x²+2f(3)=3²+2=11
f(x-1/x)=x^2-2+1/x^2+2=(x-1/x)^2+2因此有f(x)=x^2+2f(3)=9+2=11
f(x-1/x)=x的平方+1/x平方=(x-1/x)^2+2f(t)=t^2+2f(3)=9+2=11
