设x+1=tx=t-1带入(t-1)^2+2(t-1)-5 =t^2-6所以f(x)=x^2-6
令X+1为t ，则X=t-1 .原式为：f(t)=(t-1)的平方+(t-1)-5就这样…化简一下…
x∧2+2x-5=(x+1)^2-6f(x)=x^2-6
f(x+1)=x∧2+2x-5=(x+1)^2-6所以f(x)=x^2-6
