若x²+5y²-4xy+2y+1=0，则x²-y²=

显示全部楼层 · 2012-4-3 22:07:05

x2+5y2-4xy+2y+1=0(x2-4xy+4y2)+(y2+2y+1)=0(x-2y)2+(y+1)2=0所以x=2y y=-1x=-2x2-y2=4-1=3...

千问 · 2012-4-3 22:07:05

x2+5y2-4xy+2y+1=0(x2-4xy+4y2)+(y2+2y+1)=0(x-2y)2+(y+1)2=0(x-2y)2=0 (y+1)2 =0x=2y=-2y= -1x2-y2=3...

千问 · 2012-4-3 22:07:05

(1)x^2+5y^2-4xy+2y+1=0x^2-4xy+4y^2+y^2+2y+1=0(x-2y)^2+(y+1)^1=0则x-2y=0,y+1=0 -> x=-2,y=-1 -> x^2-y^2=(-2)^2-(-1)^2=4-1=3 (2)a^2+b^2+c^2+ab+bc+ac=1/2*(2a^2+2b^2+2c^2+2ab...

千问 · 2012-4-3 22:07:05

x2+5y2-4xy+2y+1=0(x-2y)2+(y+1)2=0则：x-2y=0y+1=0解得：x=-2；y=-1x2-y2=4-1=3 若a+b=3,b+c=4,a+c=5.则a2+b2+c2+ab+bc+ac=(1/2)(2...

千问 · 2012-4-3 22:07:05

若x2+5y2-4xy+2y+1=0则(x-2y)2+(y+1)2=0∴x=2y,y=-1∴x=2y=-2∴x2-y2=4-1=3 a+b=3,b+c=4,a+c=5.则a2+b2+c2ab+bc+ac=1/2[(a+b)2+(b+...