a(x+1)^2+b(x+1)+c=ax^2+(2a+b)x+a+b+c=3x^2-4x+7
a=3 ----------------------------(1)
2a+b = -4, -------------------(2)
a+b+c= 7 ---------------------(3)
(1) 代入 (2) 得:b=-4-2a=-10
把 a=3, b=-10 代入(3) 得:3-10+c=7
c=14
c-a+b=14-3-10=1
a(x+1)^2+b(x+1)+c=ax^2+(2a+b)x+a+b+c=3x^2-4x+7
a=3 ----------------------------(1)
2a+b = -4, -------------------(2)
a+b+c= 7 ---------------------(3)
(1) 代入 (2) 得:b=-4-2a=-10
把 a=3, b=-10 代入(3) 得:3-10+c=7
c=14
c-a+b=14-3-10=1