Posted by Anon on Friday, January 20, 2012 at 1:54pm.
I don't even how to go about this....
Mars is in an elliptical orbit with the Sun at one focus, as shown in the figure. At its aphelion, Mars is 156 million miles from the Sun. At its perihelion, Mars in only 128 million miles from the Sun.
How long is the major axis of the ellipse?
What is the major radius?
Find the focal radius.
Find the minor radius (round to the nearest hundredth).
Find the eccentricity (round to the nearest thousandth).
Write a Cartesian equation.
A planet's equinox (equal day and night) occurs when the angle at the Sun between the major axis and the planet is 90o. How far from the Sun is Mars on the equinox? (Round to the nearest hundredth.)
How far from the Sun are the directrices of the ellipse? (Provide either one of the two directrices rounded to the nearest whole number.)
Write parametric equations for the ellipse.
This looks like Greek to me. .

Precalculus  Reiny, Friday, January 20, 2012 at 3:17pm
You must be studying the ellipse, therefore, must be familiar with the properties of an ellipse such as the a and b values
Can we assume that Mars is at one of the focal points of the elliptical path?
2a = 156+128 = 284
a = 142
c = 142128 = 14
Calculate major radius etc, as defined in your text.
eccentricity = 14/142 = .0986
also b^2 + c^2 = a^2
b^2 + 14^2 = 142^2
b^2 = 19968
b = √19968 = 141.308
equation:
x^2 / 142^2 + y^2 / 141.308^2 = 1
at equinox, x = 14
14^2/142^2 + y^2/141.308^2 = 1
y^2 / 141.308^2 = .990279706
y^2 = 19773.905
y = 140.62
So it is 140.62 million miles from the sun.
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