y=x+m
x²/4+(x+m)²=1
x²+4x²+8mx+4m²=4
5x²+8mx+4m²-4=0
Δ=64m²-80m²+80=16(5-m²)
(1)相交
Δ=16(5-m²)>0
5-m²>0
-√5(2)相切
Δ=16(5-m²)=0
5-m²=0
m=±√5
(3)相离
Δ=16(5-m²)<0
5-m²<0
m<-√5或者m>√5