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given the system of equations y=x^2-4x x=4 the number of points of intersection is

 May 25, 2015

Best Answer 

 #4
avatar+27531 
+13

Melody, You use the "Input" line below the graph.  Just type in y=x^2-4*x and press Enter.  Similarly for x=4.

 May 26, 2015
 #1
avatar+981 
+10

y = x² - 4x      x = 4

 . . . I think this means when the lines cross. So the answer is 1 I think.

 

When x=4 . . . y = 4^2 - 4*4 = 0

 

Since y = x² - 4x is a parabola, it only ever crosses any x coordinate once. I think I'm making sense at least.

 May 25, 2015
 #2
avatar+99272 
+8

Hi Zac,

I didn't know that could be graphed in GeoGebra !

I use the download version - you seem to be using the online version, I wonder if it makes a difference?

Where did you go to graph the equations? I mean how did you do it?

 

Oh - Sorry Zac, yes, your answer makes perfect sence :)

 May 25, 2015
 #3
avatar+981 
+5

Yeah I also have the download version.

 May 26, 2015
 #4
avatar+27531 
+13
Best Answer

Melody, You use the "Input" line below the graph.  Just type in y=x^2-4*x and press Enter.  Similarly for x=4.

Alan May 26, 2015
 #5
avatar+99272 
+8

Thanks Alan, I had never seen that input bar before   

Anyway now, thanks to you and Zac, I have another cool tool!     

Do you know if you can put restrictions on the domain or range?

like can I graph y=x^2   for  -3<x<2   ?

 May 26, 2015
 #6
avatar+98091 
+3

Yeah....thanks, Alan........I always wondered how to generate a graph in GeoGebra.......!!!!

 

 

 May 26, 2015
 #7
avatar+99272 
+3

Yes, me too Chris :)

 May 26, 2015
 #8
avatar+27531 
+8

You can put limits on as follows.  In the Input bar type:  If(-3<x<2,x^2,NaN) 

This results in:

Geogebra graph:

(I changed the colour myself - the default is black).

 

I should note:

1. The If statement is in the form If(condition, result if condition is true, result if condition is false);

2. NaN stands for Not A Number.

.

 May 26, 2015
 #9
avatar+99272 
+3

Thanks Alan, what does NaN stand for?

 May 26, 2015
 #10
avatar+27531 
+8

See my edit above.

 

NaN (Not A Number) is commonly used in many computer languages to represent an undefined region of a function.

.

 May 26, 2015
 #11
avatar+99272 
+3

Thanks Alan,  that is really neat.  I mean the true false condition.  I like that  

 May 26, 2015
 #12
avatar+99272 
+8

I have just added this to the calculator/ other resources section of our Reference Material sticky thread.

GeoGebra was already there.  I have added this underneath  

 May 26, 2015

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