Sine function root points "undefined"?

Stefan shared this question 7 months ago
Answered

Hi, when I enter a sine function like f(x)=3sin(x) i can use root command to find the root points.


But when I enter a range like f(x)=3sin(x), 0<=x<=4 then root returns "undefined".


What am I doing wrong?

Comments (2)

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Salut Stefan,


the reason is that the root(s)-command in this form only works for polynomials.

Look here: https://wiki.geogebra.org/en/Root_Command and https://wiki.geogebra.org/e...


So you have to add a start-value.


You can see in the attached file the effects of the restriction of the domain of the sine function by finding roots.


I know that this is mind-boggling, because you are expecting, that GeoGebra should "know" the roots like you do.

But indeed, sometimes GeoGebra is dumb as a rock.


Greetings

mire2

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Thank you for your help with this, effectively I didn't know that limitation. It is peculiar, I thought geogebra calculates the roots even if I limit the scope to a certain range.


For those interested, if you use the menu a lot and select "crossing with object" from the menu twice (once per root point!) it will calculate the root points in my example just fine. What is even more odd is that Geogebra doesn't find the second root at first try. You have to click twice (or use the root function like Mire2 stated).

You just cannot select "root" from the menu for a function with limited scope like my example.

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