Page 1  Equations
Eccentricity: To use the equation you must be able to look at a diagram, know which value is d (distance between foci) and which is L (length of major axis), and then make measurements. Knowing the equation without knowing what d and L are and how to find them is absolutely worthless! 

The illustrations (above)
show the orbit of a planet, X, going around a star. There are 2 foci
(red dots). The star is at one of the foci. As seen
in the second illustration, 'd' is the distance between foci (red
line). You will have to measure that distance using the ruler on
page one of your ESRT. In the third illustration (right) you will see
the major axis (blue line). You must measure the major axis just as
you measured 'd'. Now, using the equation, put d over L and divide to get e (eccentricity). Things to remember: > e is just a number. It has no units so don't ever use units for eccentricity. > e must be a number between 0 and 1. If you ever get a value for e that is greater than 1 it's because you put L over d instead of d over L. Correct your mistake! 

Density: Know the definitions of mass and volume: Mass: amount of matter in an object. Volume: amount of space occupied by an object. Know units: Mass is in grams (g) or kilograms (kg) Volume is in liters (l), milliliters (ml) or cubic centimeters (cm3). Units for density are the mass unit over the volume unit. Example: if mass is in grams and volume is in milliliters, then density is expressed as g/ml. 
For help with 'Gradient' and 'Rate of Change' see this powerpoint....
