Question

A=2a²-a B=-5a＋1 当a=-二分之一时，3A-2B＋1的值？

已知x-y=﹣3求（x-y)²-3x＋3y＋1的值

Answer 1

解：
3A-2B＋1
=3(2a²-a)-2(-5a+1)+1
=6a²-3a+10a-2+1
=6a²+7a-1
把a=-1/2代入上式
=6×(-1/2)²+7×(-1/2)-1
=3/2-7/2-1
=-3
(x-y)²-3x＋3y＋1
=(x-y)²-3(x-y)+1
把x-y=-3代入上式
=(-3)²-3×(-3)+1
=9+9+1
=19

Answer 2

a=1/2
A=1 B=7/2
3A-2B＋1=3-7+1=-3

（x-y)²-3x＋3y＋1
=（x-y)²-3(x-y)＋1
=9+9+1
=19

Answer 3

因为x-y=﹣3所以（x-y)²-3x＋3y＋1=（x-y)²-3（x-y)＋1=(-3)²-3(-3)+1=19