(dy/dx)=(y(2-3x))/(x(1-3y))​

The equatorial radius of the planet Mars:
r = 3.396 km
An arc of the planet that is visible to a camera in a satellite:
cos Ф/2 = r / ( r + 12,000 ) = 3.396 / ( 3,396 + 12,000 ) = 
= 3,396 : 15,396 = 0.22
Ф/ 2 = cos^(-1) 0.22 = 77.3°
Ф = 2 · 77.3° = 154.6°
154° 36 `