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A certain ellipse is tangent to both the \(x\)-axis and the \(y\)-axis, and its foci are at \((2, -3 + \sqrt{5})\) and \((2, -3 - \sqrt{5})\) Find the length of the major axis.

 May 7, 2019
 #1
avatar+111455 
+1

The major axis will lie parallel to the y axis

So we have this form   :  (y - k)^2   +  (x - h)^2

                                       _______       _______   =    1

                                          a^2                b^2

 

 

The center of the ellipse  is  (2, - 3)  = (h, k)

Since the ellipse is tangent to the y axis and (2, -3) is the center.....then the minor axis must be 4 units in length

So  b = 4/2  = 2   and b^2  = 2

 

And we can find "a" thusly :   a^2 - b^2  = c^2

a^2  = ???

b^2 = 4

c^2 = (√5)^2  = 5

So

a^2 - 4 = 5

a^2  = 9

a = 3

 

And the major axis  = 2a  = 2(3)  = 6

 

Here's a graph : https://www.desmos.com/calculator/iagepa6zop

 

 

 

cool cool cool

 May 7, 2019
 #3
avatar+171 
-1

Thanks only thing what "thusly" is that a math term I should know or is it just like a therefore. I know it is a dumb question I should know the answer to.

 May 13, 2019

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