由题可知f(x)是二次函数设f(x)=ax^2+bx+cf(x-1)=a(x-1)^2+b(x-1)+c=ax^2-2ax+a+bx-b+c=ax^2+(b-2a)x+a-b+c2f(x)+f(x-1)=2ax^2+2bx+2c+ax^2+(b-2a)x+a-b+c=3ax^2+(3b-2a)x+a-b+3c3a=13b-2a=0a-b+3c=0a=1/3 b=2/9 c=-1...