|
Welcome Guest | Login | |
|
Index
| Recent Threads
| Who's Online
| Register
| Search
| Help
| 
|
 |
WebGraphing.com Forum » List all forums » Forum: Precalculus and Trigonometry Homework Help » Thread: PARABOLA PROBLEMS |
|
Total posts in this thread: 2 |
[Add To My Favorites] [Watch this Thread] [Post new Thread] |
| Author |
|
4237183
|
Could you please help me out with one more problem? Find the equation in the standard form of the parabola with directrix x=5 and focus (11, -7). This is another one where I don't know how to begin. Can't find any example problems in my textbook to help me out either. Thank you! |
||
|
|
pskinner
Joined: Apr 2, 2005 Posts: 797 Status: Offline |
One standard form, when the directrix is is of the form x=h-p, where (h,k) is the vertex, is: (y-k)^2=4p(x-h) Visually, this is a parabola that opens to the right or left (p>0 or p<0, respectively). Either way, the focus is (h+p,k). You are given: (h+p,k)=(11,-7), so k=-7 and h+p=11. Also, the directrix is given by x=5 and x=h-p, so h-p=5 Solving the two equations in h and p, say, by adding, get 2h=16 so h=8. Substituting back, get p=h-5=8-5=3. Putting this all together, (y-(-7))^2=4(3)(x-8), or (y+7)^2=12(x-8) ---------------------------------------- Principal Skinner ---------------------------------------- [Edit 1 times, last edit by pskinner at May 17, 2007 10:00:56 PM] |
||||
|
| [Show Thread Printable Version] [Post new Thread] |
Re: PARABOLA PROBLEMS