x^4-y^2=4
(x^2-y)(x^2+y)=4
x的四次方减Y的平方=4
(X的平方+Y)(X的平方-Y)=4
x^4-4=(x^2-2)(x^2+2)=(x-根2)(x+根2)(x^2+2)
x^4-y^2=4 (x^2-y)(x^2+y)=4