（x+y)的4次方--（x--y)的4次方

显示全部楼层 · 2012-2-9 16:46:29

（x+y)的4次方--（x--y)的4次方=[（x+y）2+（x-y）2][（x+y）2-（x-y）2]=(x^2+2xy+y^2+x^2-2xy+y^2)(x+y+x-y)(x+y-x+y)=2(x^2+y^2)2xy=4(x^2+y^2)xy...

千问 · 2012-2-9 16:46:29

原式=[(x＋y)2＋(x－y)2]×[(x＋y)2－(x－y)2]
=[2x2＋2y2]×[4xy]
=8xy(x2＋y2)...

千问 · 2012-2-9 16:46:29

（x+y)的4次方--（x--y)的4次方=[(x+y)2+(x-y)2][(x+y)2-(x-y)2]=﹙2x2＋2y2﹚﹙x+y+x-y)(x+y-x+y)=8xy(x2＋y2﹚...

千问 · 2012-2-9 16:46:29

(x+y)^4-(x-y)^4=【（x+y）^2+（x-y）^2】【(x+y)^2-(x-y)^2】=（x^2+2xy+y^2+x^2-2xy+y^2）(x^2+2xy+y^2-x^2+2xy-y^2)=2（x^2+y^2）(4xy)=8xy(x^2+y^2)...

千问 · 2012-2-9 16:46:29

(x+y)4-(x-y)4=[(x+y)2+(x-y)2][(x+y)2-(x-y)2]=(x^2+y^2+2xy+x^2+y^2-2xy)(x+y+x-y)(x+y-x+y)=2(x^2+y^2)2x*2y=8xy(x^2+y^2)...