SOLUTION: what's the center and foci of the ellipse (x+5)^2/9 +(y-7)^2/25=1

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Question 310657: what's the center and foci of the ellipse (x+5)^2/9 +(y-7)^2/25=1
Answer by Edwin McCravy(20059) About Me  (Show Source):
You can put this solution on YOUR website!


There are two types of equations for ellipses

%28x-h%29%5E2%2Fa%5E2%2B%28y-k%29%5E2%2Fb%5E2=1

where the ellipse looks like the cross section of an egg
resting on a table.

and

%28x-h%29%5E2%2Fb%5E2%2B%28y-k%29%5E2%2Fa%5E2=1

where the ellipse is upright like the number zero "0".

In either case a is half the major axis and b is half the minor axis.

The major axis is always larger than the minor axis.  So a > b.

In the case where  a = b, the ellipse is a circle.

The center is the point (h,k).  The foci are two points 

inside the ellipse on the major axis which are c units from the 

center, where c is gotten from the equation c%5E2=a%5E2-b%5E2.

Your ellipse

%28x%2B5%29%5E2%2F9+%2B%28y-7%29%5E2%2F25=1

is the type that is upright like the letter zero "0", because the
larger denominator is under the term in y.  So we compare it to

%28x-h%29%5E2%2Fb%5E2%2B%28y-k%29%5E2%2Fa%5E2=1

and we see that h=-5, k=7, a%5E2=25 so a=5 and b=3

So the center is (-5,7), the major axis is 2*5 or 10 and the minor
axis is 2*7=14, so we draw the graph:



We draw in the major and minor axes, which cross at the center:



The foci are on the major axis and are c units above and
below the center.  We calculate c

c%5E2=a%5E2-b%5E2
c%5E2=5%5E2-3%5E2
c%5E2=25-9
c%5E2=16
c=4

So the foci are 4 units directly above and below the center (-5,7).

One focus is at (-5,11) and the other is at (-5,3)




You didn't ask for the vertices and the co-vertices.

They are at the ends of the major and minor axes.

The vertices are (-5,2) and (-5,12)
The covertices are at (-8,7) and (-2,7)

Edwin