1 f(x)=x^2+2x+a
则f(bx)=b^2x^2+2bx+a=4x^2-4x+1
故b^2=4 2b=-4 a=1
故b=-2 a=1
f(x)=x^2+2x+1=(x+1)^2
f(ax+b)=f(x-2)=(x-2+1)^2>0
故x不等于1
2 记a=ln(1+1/2)+ln(1+1/3)+.ln(1+1/n)-ln(n)
则e^a=(1+1/2)(1+1/3)...(1+/n)/n
=[3/2*4/3*...*(n+1)/n]/n
=(n+1)/2n
故lim(n趋近正无穷)e^a=1/2
故lim(n趋近正无穷)a=ln1/2