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October 31, 2014

October 31, 2014

Posted by **Graham** on Saturday, January 14, 2012 at 5:34pm.

It is a hyperbola equation

(y-4)^2/49 - (x-6)^2/72 = 1

1.It is a vertical hyperbola, correct?

2. the a^2 is 49, correct?

3. the b^2 is 72, correct?

4. I find the foci by a^2 + b^2 = c^2, and when I have the square root of "c^2" it would be ( "h" which is 6 in this case, k which is 4 +-whatever "c" ended up to be, correct?

5.Vertices for vertical hyperbola is (h,k+-a), correct

- Algebra II-Please check fpr explanation -
**Graham**, Saturday, January 14, 2012 at 5:35pmI forgot one question-in a hyperbola, the "a^2" is always under the first variable, whether it be "x" or "y", correct

- Algebra II-Please check fpr explanation -
**Reiny**, Saturday, January 14, 2012 at 6:37pm1. correct

2. and 3.

I always associate a^2 with the x's

and b^2 with the y's, but that is a personal choice.

It will depend how your text or your instructor chooses.

regarding your comment, ...

what if I simply changed the equation to

(x-6)^2/72 - (y-4)^2 /49 = -1 , (which is the preferred method of writing it)

would you now label a^2 as 72 ?

Can you see the problem ?

That is why associating a^2 with the x's and b^2 with the y's makes so much more sense.

4. c^2 = a^2 + b^2 = 121

c = 11

foci : (6, 15) and (6, -7)

(your formula for a vertical hyperbola is correct)

- Algebra II-Reiny-Please check fpr explanation -
**Graham**, Saturday, January 14, 2012 at 7:10pmSo if I change the formula to = (-1), then I have to change the a^2 to be under the "x" is that correct?

Thank you for your help

- Algebra II-Please check fpr explanation -
**Reiny**, Saturday, January 14, 2012 at 8:40pmAll I did was to multiply each term by -1

I like to have all my conic section equations in standard form, that is ,

my circle, ellipse and hyperbola equations start with the "x" term.

As I said, I associate the a^2 with the x's and the b^2 with the y's.

This saves a lot of confusion.

However, if your instructor wants you to do it otherwise, such as the a's always going with the major axis, then do so.

- Algebra II-Please check fpr explanation -
**Graham**, Saturday, January 14, 2012 at 9:22pmokay-thank you I got it now

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