如楼上所讲，一种开口向左，一种开口向下！
有两种情况1、y^2=-2px p=4 y^2=-8x2、x^2=-2py p=1/2 x^2=-y
1、y^2=-2px p=4 y^2=-8x2、x^2=-2py p=1/2 x^2=-y
