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GeoGebra Topic Question Italian

Bug in calcoli tra angoli

jumpjack shared this question 3 years ago

Answered

Utilizzo Geogebra desktop 6.0.564.0.

Ho un valore E calcolato graficamente come angolo in gradi tra due segmenti.

Devo calcolare un altro angolo secondo la formula:

M = E- e * sin (E)

con "e" compreso tra 0 ed 1. Quindi M dovrebbe venire poco minore di E.

Invece, se per esempio E vale 76.3072° ed "e" vale 0.6, (adimensionale) viene fuori che M vale 0.7489!

Cioè secondo geogebra:

76.3072 - 0.6 * sin(76.3072) = 0.7489

Invece secondo la matematica:

76.3072 - 0.6 * 0.97157 = 0.7489

76.3072- 0.582942 = 75.724258

Cioè praticamente Geogebra decide di trasformare automaticamente il 76.3072 da gradi a radianti prima di fare il calcolo...

Decisamente sbagliato!

In pratica, per far tornare i conti, devo usare l'assurda formula:

76.3072 - (0.6 * sin(76.3072))*3.14/180

...perchè in realtà Geogebra "fa finta" di usare il numero 76.3072 , ma in realtà internamente usa l'equivalente in radianti 1.13311!!

E naturalmente a causa di conversioni e arrotondamenti mi perdo anche qualche decimale di precisione: il risultato vero è 75.7243 ma Geogebra dà 75.7627.

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Comments (7)

ccambre ● 3 years ago

mostraci il filo per favore

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jumpjack ● 3 years ago

https://www.geogebra.org/cl...

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Michael Borcherds ● 3 years ago

Cioè praticamente Geogebra decide di trasformare automaticamente il 76.3072 da gradi a radianti prima di fare il calcolo...

Degrees are already in radians. (360° is the same as 2pi) so it's correct

You can write E/° if you want to "lose" the degree conversion factor

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jumpjack ● 3 years ago

"Degrees are already in radians" is not an acceptable statement for a scientific software!!

Numbers are numbers, they are not supposed to "internally contain" formulas.

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ccambre ● 3 years ago

The option "Degrees or Radians" affects just how angles are diplayed, not how software works, the same as forlogaritms. Standard in programmation are radians and natural logaritms, but you can set your interface so that results are shown in degrees or log_10. Do you think that calculators have a split calculation for calculation in degrees or radians? It's indeed as simple as "360° is the same as 2pi" so users don't have to make conversions themselves.

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jumera ● 3 years ago

"...for a scientific software!!"

scientific..? ok... 45° - 1° = 44°, 0.785 - 1 = -0.214 (45° = 0.785 radians), but tell me what is the result of

45° - 1 ?

44° or -0.214 ?

(or perhaps, if you are a mathematics teacher, you says at the student who write 45° - 1 that it is an impossible calculation ?)

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Michael Borcherds ● 3 years ago

"Degrees are already in radians" is not an acceptable statement for a scientific software!!

You are arguing with 360° = 2pi?

GeoGebra is designed to work according to this and won't be changed. Once you understand that ° is not a unit and just means "multiply by 2pi and divide by 360" then it should make sense :)

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