Find equation of ellipse

[joeyjon]

Find equation of ellipse with foci (0, + or -2) length of minor axis 3---


So half the length of the minor axis is 1.5.

f squared = a squared - 1.5 squared

4 = a squared - 2.25
a squared = 6.25 (major axis)

(x squared / 6.25) + (y squared / 2.25) = 1

6.25x squared + 2.25y squared = 14.0625

The book says the answer is ---

100x squared + 36y squared = 225

 

[JeffM]

A hint: try multiplying your equation by 16.

 

[joeyjon]

wow. How about that

They must be doing it a different way, though to get that other answer.

what about the extra 225.04 that I come up with. Maybe I have my calculator set wrong?

 

[joeyjon]

I see that the answers are probably the same now, but am I missing something fundamental when I do it, in order to get their cleaner answer?

 

[joeyjon]

Ok...

I think the best thing to do (what I am going to do unless there is a better idea out there) when I see an ugly looking equation like this, I will take the decimal and use that as the divisor of 1, then the answer I get I will see if it makes the rest of the equation look pretty...

1 / .0625 = 16

then multiply the whole equation.

Thanks for your help guys!

 

[JeffM]

There was nothing wrong with your answer.

The two answers were logically equivalent