g(2x-1)=f(x^2-1)=2(x^2-1)+3=2x^2+1
令t=2x-1,所以x=(t+1)/2
所以个g(2x-1)=g(t)=2[(t+1)/2]^2+1=(1/2)*t^2+t+3/2
所以 g(x)==(1/2)*x^2+x+3/2
法二:令t=2x-1,所以x=(t+1)/2
g(2x-1)=g(t)=f[(t^2+2t+1)/4-1]
=f[(t^2+2t-3)/4]
=[(t^2+2t-3)/2]+3
=(1/2)*t^2+t+3/2
所以 g(x)==(1/2)*x^2+x+3/2