大米花0
幼苗
共回答了18个问题采纳率:100% 举报
1.x^3+y^3+3xy=(x+y)(x^2-xy+y^2)+3xy
=(x^2-xy+y^2)+3xy
=(x+y)^2
=1
2.因为x^2-y^2=2xy
得 x^2-y^2-2xy+y^2-y^2=0
∴(x-y)^2-2*y^2=0
得(1),x-y=√2y
x=(√2+1)y
(2),y-x=√2y
x=(1-√2)y
由于x,y为正数,所以解为(1).
(x-y)/(x+y)=(√2+1-1)y/(√2+1+1)y
=√2/(√2+2)
1年前
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