∵4x2+12xy+9y2=1 ∴ (2x+3y)ˆ2=1
∵x2+2xy+y2-4=0 ∴ (x+y)ˆ2=4
∵4x2-9y2=0 ∴ (2x+3y)(2x-3y)=0
∵x2-2xy+y2-1=0 ∴ (x-y)ˆ2=1
下面自己解