# Calculators Graphing help - Ti89: How to graph x^2 + y^2 = 4, etc

1. Jul 13, 2011

### nukeman

1. The problem statement, all variables and given/known data

I am working on these problems, systems of equations and inequalities. Now, I know how to do the problem and find the solution set, but our teacher said that we can check our answer by graphing it with out graphing calcs.

I have a Ti89 Titanium. How do I input/graph the following with my ti89:

x^2 + y^2 = 4
x^2 + 2x + y^2 = 0

Any help would be great! Thanks guys

2. Relevant equations

3. The attempt at a solution

2. Jul 13, 2011

### HallsofIvy

Do it as two separate functions:
$$y= \sqrt{4- x^2}$$
$$y= -\sqrt{4- x^2}$$

$$y= \sqrt{x^2+ 2x}$$
$$y= -\sqrt{x^2+ 2x}$$

Or, set "mode" to parametric equations and use
$$x= 2 cos(t)$$
$$y= 2 sin(t)$$

and, since $x^2+ 2x+ y^2= x^2+ 2x+ 1- 1+ y^2= (x+ 1)^2+ y^2- 1= 0$
gives $(x+ 1)^2+ y^2= 1$
set "mode" to parametric equations and use
$$x= -1+ cos(t)$$
$$y= sin(t)$$

Last edited by a moderator: Jul 13, 2011
3. Jul 13, 2011

### nukeman

I am not quit getting this here.

Lets do this one. Its for one I am more stuck on than the rest.

"Graph each system of Linear inequalities"

x + y = 2
2x + y = 4

How would I input this on my calc. I am finding the overlapping region, as that is the solution.

?

4. Jul 13, 2011

### gb7nash

Solve for y in both equations. You should know how to plot lines by now. After you plot the lines, you can verify that you have the correct solution by seeing where the lines intersect.

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Also, reading from your original post, doesn't your teacher want you to check the answer without using a calculator? Being able to type it into your TI-89 is moot.

5. Jul 13, 2011

### Trevormbarker

just isolate y, set equal to eachother and solve for x, That will probably take much less time then graphing and finding the point of intersection

6. Jul 13, 2011

### gb7nash

From reading the original post, it looks like nukeman already knows how to find the solution. I think he's just trying to graph the equations.

7. Jul 13, 2011

### Trevormbarker

your right, I didnt see that.

8. Jul 13, 2011

### QuarkCharmer

Do as HallsOfIvy said above (separating it into two equations), and then simply press:
diamond (green key) F1, to open your Y editor.
Put your equations in there, then press diamond F3 to graph. From the graph screen you can press F2 to look through the menu options and zoom in/out, or press diamond F2 to set the window manually.

If you want to just "solve" the equations, you just have to press F2 (or is it F3) and go to solve.
If you have questions about the functions like Solve/Expand/Factor and such, just press Catalog, and scroll down to find it and it will list the arguments at the bottom of the screen when it's highlighted.