8x^2+1=8t^2/(1-2t^2)^2 +1=(8t^2+1-4t^2+4t^4)/(1-2t^2)^2 =(4t^2+1+4t^4)/(1-2t^2)^2 =(1+2t^2)^2/(1-2t^2)^2 =(1/y)^2化为一般方程为8x^2y^2+y^2=1
