2/1x²+2/7x+5=0 两边乘2x²+7x+10=0(x+5)(x+2)=0x=-5,x=-1(x²+y²)(x²+y²+1）=20 令a=x²+y²a(a+1)=20a²+a-20=0(a+5)(a-4)=0a=-5,a=4a=x²+y²≥0所以x²+y&...