2207是最后结果,在前面式子中除以x可得到x+1/x,再在后面的
x^4+1/x^4
=(x^4+1/x^4+2)-2
=(x^2+1/x^2)^2-2
=(x^2+1/x^2+2-2)^2-2
=[（x+1/x)^2-2]^2-2
=[7^2-2]^2-2
=2207