Question

2（x-2y)二次方+4（2y-x)-(x-2y)二次方+3(x-2y)，其中x=负二分之一，y=二分之一

化简求值

Answer 1

2（x-2y)二次方+4（2y-x)-(x-2y)二次方+3(x-2y)，
=2(x-2y)²-4(x-2y)-(x-2y)²+3(x-2y)
=(x-2y)²-(x-2y)
=(-1/2+1)²-(-1/2+1)
=1/4-1/2
=-1/4

追问

错了吧，我觉得应该是
2（x-2y)二次方+4（2y-x)-(x-2y)二次方+3(x-2y)，
=2(x-2y)²+4(x-2y)-(x-2y)²+3(x-2y)
=2(x-2y)²-(x-2y)²+4(x-2y）+3(x-2y)
=(x-2y)²+7(x-2y)
=(-1/2-1)²+7*(-1/2-1)
=9/4-7/2
=-5/4

追答

4(2y-x)=4[-(x-2y)]=-4(x-2y)

(2y-x)²=[-(x-2y)]²=(x-2y)²

Answer 2

=2(x-2y)(x-2y)-2x+8y+(x-2y)(x-2y)+3x-2y
=4x的二次方-8y的二次方-2x+8y+x的二次方-4y的二次方+3x-2y
=5x的二次方-12y的二次方+x+6y
=-5/4-3-1/2+3
=3/4