X二次方=3XY-4Y方=0（Y≠0）求X+Y分之X-Y

X²+3XY-4Y²=0
(X+4Y)(X-Y)=0
X=-4Y,X=Y

若X=-4Y,(X-Y)/(X+Y)=(-4Y-Y)/(-4Y+Y)=-5Y/(-3Y)=5/3
若X=Y,(X-Y)/(X+Y)=(Y-Y)/(Y+Y)=0

x^2+3xy-4y^2=0
(x+4y)(x-y)=0
x+4y=0或x-y=0
(1)x+4y=0,x=-4y
(x-y)/(x+y)=(-4y-y)/(-4y+y)=-5y/-3y=5/3
(2)x-y=0,x=y
(x-y)/(x+y)=0

x^2+3xy-4y^2=(x+4y)(x-y)=0
x=-4y,或，x=y

x=y时，X+Y分之X-Y=0
x=-4y时，X+Y分之X-Y=-5y/(-3y)=5/3