(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

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