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rad/degree error in geometry app?
09-17-2015, 07:28 PM
Post: #1
rad/degree error in geometry app?
Hello,
I guess I found a slight error in the geometry app. I added four random points and connected them to three segments. Doing some measurenemts I wanted to measure the angle of the segments.
So I added the angle feature and selected the points. I got my Prime usually set up in rad mode but using the geometry app I set it to degree mode.
The angle which was displayed after selecting the points was in rad, but it should be in degrees.
After switching to the apps menu and back to the geometry plot everyting was correct.
So to get the degrees I have to switch to the apps and back to the geometry app.
If I add a new angle all other angles will be displayed in rad again until I switch to the apps and then back to the geometry app.

Greetings
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09-18-2015, 03:11 AM
Post: #2
RE: rad/degree error in geometry app?
(09-17-2015 07:48 PM)Spybot Wrote:  By other hand, I also traced some segments and tried to measure some angles and this is what I got, angle measurements don't logically match with the actual graph.

In using the Measurement>Angle command, you have to specify the vertex first. I'm not sure why it's set up like that, it seems like most mathematical conventions specify angles using the convention you have chosen.

Brad
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09-18-2015, 01:11 PM
Post: #3
RE: rad/degree error in geometry app?
I don't have any clue either. Bernard set it up that way long before we started using the CAS in prime. Maybe he can shed some light...

TW

Although I work for the HP calculator group, the views and opinions I post here are my own.
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09-18-2015, 03:42 PM
Post: #4
RE: rad/degree error in geometry app?
Not sure what you mean.
angle(A,B,C) computes the angle of AB and AC (oriented angle).
Maybe you would have preferred the syntax angle(B,A,C)?
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09-18-2015, 05:16 PM
Post: #5
RE: rad/degree error in geometry app?
(09-18-2015 03:42 PM)parisse Wrote:  Not sure what you mean.
angle(A,B,C) computes the angle of AB and AC (oriented angle).
Maybe you would have preferred the syntax angle(B,A,C)?

I think what people are expecting is the syntax BAC (the vertex is the middle between the two other points. I don't think I've ever seen any geometric diagrams that don't place the vertex in the middle. Ex: "angleABC is 45°", the point "B" is where the angle is.

I wonder if this is another regional thing?

TW

Although I work for the HP calculator group, the views and opinions I post here are my own.
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09-19-2015, 06:27 AM
Post: #6
RE: rad/degree error in geometry app?
I think it's more about directed angle or not, at least in France we are using the notation (AB,AC) for the directed angle of apex A, and hat{BAC} for undirected angle. Most school teachers are probably expecting angle measure to be undirected angle with A in the middle, and that's probably the reason why geometry software choosed this argument ordering.
I don't want to change the ordering for giac, but nothing prevent us from adding another command with the undirected ordering, for example ANGLE(B,A,C) would return angle(a,b,c), and the geometry app could use ANGLE.
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