## Re: Graphing Rotation of ellipse

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# Re: Graphing Rotation of ellipse

```On Wed, 15 Apr 1998, William Walters wrote:

> Can anyone tell me how to graph the following ellipse:
>
>    7X^2 - 6sqrt(3)XY + 9Y^2 - 16 = 0
>
> I have a TI-82 and a TI-83 for classroom demos and a personal TI-85, but
> would prefer not to use it.  If there is no way on the TI's, is there a
> graphical program for the computer?
>
> Bill Walters
> Poca High School
> Poca, WV
>
easiest way:
in FUNC mode,
use the quadratic formula to solve for Y in terms of X:
Y1 = (6root3X+{-1,1}root(36*3X^2-36(7X^2-16)))/18
After experimenting a bit, xMin = -3,  xMax = 3, yMin = -1
yMax = 1    and then ZOOM SQUARE.

I also have a program that will accept the coef of a general quadratic and
then do a rotation of coordinate system to get a standard form.  Then, in
parametric form, graph the conic. The program displays theta and coef of
standard eq. The graph does not have any "holes" in it like the quadratic
formula/FUNC mode method above.  But, except for a higher level class, you
do not need the rotation of coordinate system complications. I'll see if I
can find that program on my computer and send it to you if you want it. I
recall writing it on an airplane trip about two years ago.
Charlie

```

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