解：换元法：设t=√x+1x=(t-1)^2f(t)=(t-1)^2+2(t-1)=t^2-1f(x)=x^2-1配方法：（√x+1）^2=x+2√x+1所以，f(√x+1)=(√x+1)^2-1f(x)=x^2-1
因为f（√x+1）=x+2√x=(√x+1)^2-1所以把√x+1用x代换掉，则f(x)=x^2-1 望采纳~
