Prove two vectors are perpendicular (2-D)

  • Context: High School 
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    Perpendicular Vectors
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Discussion Overview

The discussion revolves around proving that the vectors (ai + bj) and (-bi + aj) are perpendicular in a two-dimensional space. Participants explore various methods to demonstrate this relationship without using the scalar product, as it has not been introduced in the context of the problem.

Discussion Character

  • Homework-related
  • Mathematical reasoning
  • Conceptual clarification

Main Points Raised

  • One participant expresses confusion and requests hints on how to approach the problem.
  • Another participant suggests constructing a triangle with the vectors as sides and using trigonometry to show that they form a right angle.
  • A different participant states that two vectors are perpendicular if their dot product is zero, providing a calculation that results in zero.
  • One participant combines the triangle construction with the dot product argument, noting the constraints of the problem and attempting to apply the Pythagorean theorem to confirm the right triangle assumption.

Areas of Agreement / Disagreement

Participants present multiple approaches to the problem, including trigonometric methods and the dot product, but there is no consensus on a single method to be used given the constraints of the problem.

Contextual Notes

Participants acknowledge that the scalar product has not been introduced in their studies, which influences the methods they consider appropriate for the proof.

rbnphlp
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Show that (ai+bj)and (-bi+aj) are perpendicular...

im clueless on what to do ..any hints will be greatly apperciated
thanks
I know I am missing something really simple

Also the book has not yet introduced the scalar product so they want me to use some other way
 
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help anyone?
 
Construct a triangle with these vectors as his sides, and use trigonometry to prove that they have a right angle between them
 
Two vectors are perpendicular if their dot product is zero. For your case, the dot product is -ab+ab=0.
 
elibj123 said:
Construct a triangle with these vectors as his sides, and use trigonometry to prove that they have a right angle between them

mathman said:
Two vectors are perpendicular if their dot product is zero. For your case, the dot product is -ab+ab=0.

Thanks both of you ..the book hasn't introduced scaler product yet so I don't think they wanted me to use that method ..

I drew a triangle .. OA=(a,b)(|OA|=\sqrt{a^2+b^2}), OB=(-b,a)|OB|\sqrt{a^2+b^2} , then AB=(b+a,b-a)|AB|=\sqrt{(b+a)^2+(b-a)^2}
then I assumed it to be a right triangle and used pythagoras
i.e and is easily shown |OB|^2+|OA|^2=|AB|^2 ..
I hope this proof is right thanks
 

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