f(x)=a×lg×[x+Sqrt(1+x^2)]-x^2
=a*lg[x+根号(1+x^2)]-x^2
=a*lg{[(1+x^2)-x^2]/[根号(1+x^2)-x]}-x^2
=a*lg{1/[根号(1+x^2)-x]}-x^2
=-a*lg[根号(1+x^2)-x]-x^2
令g(x)=a*lg[x+根号(1+x^2)]=-a*lg[根号(1+x^2)-x]
则g(-x)=-a*lg[根号(1+x^2)+x]=-g(x),
g(x)是奇函数.
则f(x)=g(x)-x^2
f(2)=g(2)-2^2=5
g(2)=9
所以g(-2)=-9
f(-2)=g(-2)-(-2)^2=-9-4=-13