(1)f(2x+1)=x^2+2x+3令2x+1=t,则有x=(t-1)/2,则有：f(t)=(t-1)^2/4+2(t-1)+3=t^2/4-t/2+1/4+2t-2+3=t^2/4+3t/4+13/4.所以：f(x)=x^2/4+3x/4+13/4.(2)f(3x+5)=9x^2+6令3x+5=t.则有x=(t-5)/3f(t)=9*(t-5)^2/9+6=(t-5)^...