x=(100-3y)/4
(100-3y)^2/16+y^2=625
(25/16)y^2-37.5y=0
25y^2-600y=0
y1=0
y2≠0
25(y2)-600=0
y2=24
x1=25
x2=7
x=25,y=0
或：x=7,y=24