x^2/16+y^2/9=1
x=4cost
y=3sint
x+y+c
=4cost+3sint+c
=5sin(t+m)+c (其中,cosm=3/5, sinm=4/5)
而：x+y+c>=0
所以：5sin(t+m)+c>=0
c>=-5sin(t+m)
c>=5