x^2/45+y^2/20=1
a^2=45,b^2=20
c^2=a^2-b^2=25
以O为圆心,半径5的圆方程
x^2+y^2=25 1)
x^2/45+y^2/20=1 2)
1)/20 -2)
x^2/20-x^2/45=1/4
5x^2/180=1/4
5x^2=45
x^2=9
x1=3,x2=-3
y^2=16
y1=4,y2=-4
P1(3,-4) P2(3,4) P3(-3,-4) P4(-3,4)