The imaginary line that divides the earth into in this case the north and south hemispheres is called the Equator and it passes through Ecuador and actually Ecuador is the Spanish word for Equator. The French explorer La Condamine spent 10 years in Ecuador studying the equator and determined the oblate spheroid shape of the world.
You would draw a table like the above ^
And you would input each x value (1,2,3,0,-1,-2,-3) into the equation one by one for the value of both x and y
I did the first one for you so you understand how to do it.
The Mississippi-Missouri-Ohio river system is the largest and most significant river system in the world.