y=(2a^2+6)/(a^2+4)=(2a^2+8-2)/(a^2+4)=2-2/(a^2+4)(a^2+4)=2/(2-y) (1)x=a/(a^2+4)=a/2/(2-y)=a(2-y)/2a=2x/(2-y)代入(1):(2x/(2-y))^2+4)=2/(2-y)4x^2+4(2-y)^2=2(2-y)2x^2+8-8y+2y^2=2-y2x^2+2y^2-7y+6=0