Triangle law of vector addition and the Pythagoras theorem

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Discussion Overview

The discussion revolves around the triangle law of vector addition and the Pythagorean theorem, exploring their definitions, applications, and the differences between them. Participants examine how these concepts relate to each other in the context of vector addition and geometry.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants suggest that the triangle law of vector addition is distinct from the Pythagorean theorem, particularly in how they calculate resultant vectors.
  • One participant proposes that the triangle law may refer to the law of cosines, noting that it simplifies to the Pythagorean theorem when the angle is 90 degrees.
  • Another participant explains that the triangle law describes the relationship between two vectors and a resultant vector, while the Pythagorean theorem specifically calculates the length of the resultant vector without addressing direction.
  • A participant presents a specific example involving two vectors, questioning the validity of the results obtained from both the triangle law and the Pythagorean theorem.
  • One participant asserts that the Pythagorean theorem is correct and challenges the terminology of "triangle law" as used by others.
  • Another participant introduces the cosine theorem, providing a mathematical formulation that connects the triangle law to the Pythagorean theorem under certain conditions.

Areas of Agreement / Disagreement

Participants express differing views on the terminology and application of the triangle law of vector addition versus the Pythagorean theorem. There is no consensus on whether the triangle law is a valid term or concept, and the discussion remains unresolved regarding the correctness of the different approaches presented.

Contextual Notes

Some participants reference specific mathematical formulations and examples, but there are unresolved assumptions about the definitions and applications of the triangle law and the Pythagorean theorem. The discussion does not clarify the conditions under which each theorem applies.

akashpandey
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TL;DR
Triangle law of vector addition and pythagoras theorem
i know its pretty basic but please give some insight for
triangle law of vector addition and pythgoras theorem.
because ofcourse if you use traingle law to find resultant it will be different from what is pythagoras theorem
 
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akashpandey said:
Summary: Triangle law of vector addition and pythagoras theorem

i know its pretty basic but please give some insight for
triangle law of vector addition and pythgoras theorem.
because ofcourse if you use traingle law to find resultant it will be different from what is pythagoras theorem
If by "triangle law", you mean the law of cosines, check out what happens when the angle is 90 degrees.
 
akashpandey said:
Summary: Triangle law of vector addition and pythagoras theorem

i know its pretty basic but please give some insight for
triangle law of vector addition and pythgoras theorem.
because ofcourse if you use traingle law to find resultant it will be different from what is pythagoras theorem
"The triangular law" for vector addition is what happens if we add to vectors to a third vector. All have direction and length. Pythagoras is a special case of the cosine theorem. It needs a right angle, otherwise we need the cosine theorem. And even in case of a right angle, it only says something about the length of the resulting vector, nothing about direction. So "triangular law" is what happens, and Pythagoras how to calculate the length.
 
Suppose there is a vector a of magnitude 5 units to the east, another vector b of magnitude 6 units to the north. To find magnitude of vector a + vector b,
By the triangle law of vector addition, it is 5 + 6 units = 11 units.
By Pythagorean theorem, it is sqrt(5^2 + 6^2) = sqrt(61)
Which answer is right? If so, why is the other wrong?
Thank you!
 
akashpandey said:
By the triangle law of vector addition, it is 5 + 6 units = 11 units.
By Pythagorean theorem, it is sqrt(5^2 + 6^2) = sqrt(61)
Which answer is right? If so, why is the other wrong?
Pythagoras is correct. There is no such thing as the "triangle law" you have quoted.
 
Perhaps the OP has the cosine theorem in mind?

Take three points A, B, C in Euclidean space. Then you have
$$\overrightarrow{AB}+\overrightarrow{BC}=\overrightarrow{AC}.$$
Thus
$$|BC|^2=\overrightarrow{BC}^2=(\overrightarrow{AC}-\overrightarrow{AB})^2 = |AC|^2 +|AB|^2 -2 |AC| |AB| \cos(\angle{BAC}).$$
If the angle is ##\pi/2## the cosine term vanishes, and you have Pythagoras's Theorem as a special case.
 

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