this ellipse is centered at the point (-3, 2). The length of its horizontal axis is 7. What is the ellipse's equation?

here's a photo to help

http://media.apexlearning.com/Images/200407/21/90f5c30a-7756-4c37-b0ec-105a59946485.gif

possible answers either a,b, or c

A. (x+3)^2 (y-2)^2
-------- + -------
7^2 14^2= 1

B.(x+3)^2 (y-2)^2
--------- + ------- = 1
(3.5)^2 17^2

C. (x-6)^2 (y-8)^2
------- + ------ = 1
(3.5)^2 7^2

Question

this ellipse is centered at the point (-3, 2). The length of its horizontal axis is 7. What is the ellipse's equation?

here's a photo to help 

http://media.apexlearning.com/Images/200407/21/90f5c30a-7756-4c37-b0ec-105a59946485.gif

possible answers either a,b, or c

A. (x+3)^2       (y-2)^2
    -------- + -------
        7^2             14^2= 1

B.(x+3)^2         (y-2)^2
 --------- + -------  = 1
  (3.5)^2             17^2

C. (x-6)^2    (y-8)^2
   ------- + ------ = 1
     (3.5)^2         7^2

whpalmer4 · Answer

A little bit of logic can be used to eliminate some answer possibilities.  Recall that a circle is a special case of an ellipse, much like a square is a special case of a rectangle.  The formula for a circle with radius $r$ centered on $(h,k)$ is $$(x-h)^2+(y-k)^2=r^2$$

That immediately rules out C as an answer choice, because the center isn't in the right place.

dumbcow · Answer

length of horizontal  = 2a

denominator is a^2

whpalmer4 · Answer

To figure out which equation might be correct of the other two, why not set $y=0$ and see what you get for $x$?  Experimental learning, it's a good thing...

anonymous · Answer

B is the correct answer

anonymous · Answer

so the answer would be b ,correct?

anonymous · Answer

You need (x+3)^2 because of the X displacement of 3 so that rules out one of the answers, and you need 3.5^2 as that's the radius of one of the axes so that rules out the other possible choice. Test taking 101!