Answer:
addition property
Step-by-step explanation:
Please insert your equation number
Consider the attached ellipse. Let the sun be at the right focus. Then perihelion is at right vertex on the x-axis and aphelion is at the left vertex on the x-axis.
The distances:
- from perihelion to the sun in terms of ellipse is a-c;
- from aphelion to the sun in terms of ellipse is a+c.
Then

Add these two equations:
and subtract first equation from the second:
Note that
thus

The equation for the planet's orbit is

5x - 3y = -11 (×2)
2x - 6y = -14 (x5)
10x - 6y = -22
10x - 30y = -70
---------------------- -
24y = 48
y = 2