Question

(x-1/2y-1)(x-1/2y+1)-(x-1/2y+1)^2,其中x=1.5,y=3.9,先化简再求值

过程详细，请各位大神帮帮忙

Answer 1

(x-1/2y-1)(x-1/2y+1)-(x-1/2y+1)²
=(x-1/2y）²-1²-(x-1/2y+1)²
=（X-1/2y)²-1-[(x-1/2y)²+2(x-1/2y)+1]
=（X-1/2y)²-1-(x-1/2y)²-2(x-1/2y)-1
=-2-2(x-1/2y)
=-2-2x+y

把数值代入得：
原式=-2-2*(1.5)+3.9
=-2-3+3.9
=-2+0.9
=-1.1

Answer 2

原式=[(x-1/2y)-1][(x-1/2y)+1]-[(x-1/2y)+1]²
=(x-1/2y)²-1²-(x-1/2y)²-2(x-1/2y)-1
=2(x-1/2y)-2
=2x-y-2
=2*1.5-3.9-2
=-2.9

追问

(x-1/2y)²-2(x-1/2y)-1，这个不可以这样拆吧，貌似不对的感觉哎

追答

哦，对不起错了
原式=[(x-1/2y)-1][(x-1/2y)+1]-[(x-1/2y)+1]²
=(x-1/2y)²-1²-(x-1/2y)²-2(x-1/2y)-1
=-2(x-1/2y)-2
=-2x+y-2
=-2*1.5+3.9-2
=-1.1

Answer 3

提取公因式（x-y/2+1）[（x-y/2-1）-（x-y/2+1）]=-2（x-y/2+1）=-2（1.5-3.9/2+1）=-5+3.9=-1.1

Answer 4

1.2乘8.52

追问

麻烦些个过程咧