How Do You Calculate the Angle Between Two Lines?

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Discussion Overview

The discussion revolves around calculating the angle between two lines represented by their equations. Participants explore methods involving normal vectors and the dot product, as well as considerations about the appropriate forum for the topic.

Discussion Character

  • Technical explanation
  • Mathematical reasoning
  • Debate/contested

Main Points Raised

  • One participant mentions the normal vectors of the lines and questions the next steps in calculating the angle.
  • Another participant suggests that there are two forms for the dot product, one involving vector components and another involving the angle between them.
  • A participant expresses uncertainty about using the normal vector, suggesting it has the same slope, and seeks clarification.
  • One participant states that if two vectors are normal (orthogonal), their dot product will be zero and suggests using the inverse cosine function to find the angle.
  • There is a suggestion that the topic may be more appropriate for the Pre-Calculus forum, indicating a potential misplacement of the discussion.

Areas of Agreement / Disagreement

Participants express differing views on the methods to calculate the angle and the appropriateness of the forum for the discussion. No consensus is reached on the best approach or the correct placement of the topic.

Contextual Notes

There are unresolved assumptions regarding the use of normal vectors and the application of the dot product in this context. The discussion reflects varying interpretations of mathematical concepts without definitive conclusions.

Petrus
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Decide the angle between line $$x+2y-3=0$$ and $$-3x+y+1=0$$ we use ON-cordinate
progress
I know that their normalvector is $$(1,2)$$ and $$(-3,1)$$ but what shall I do next?
Is this correctly understand
33paq7r.png

Regards,
$$|\pi\rangle$$
 
Last edited:
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Re: the angle between two line

Don't you have two forms for the dot product, one involving the components and one involving the angle between them?
 
Re: the angle between two line

MarkFL said:
Don't you have two forms for the dot product, one involving the components and one involving the angle between them?
My picture did not work:S That is what I did, I just wounder if I can use the normal vector, cause normal vector got same slope if I understand correctly

Regards,
$$|\pi\rangle$$
 
Re: The angle between two line

If two vectors are normal (if I understand you to mean orthogonal or perpendicular) then their dot product will be zero. What you did was correct, you just need to solve for the angle using the inverse cosine function.

edit: Unless you are to use some other method to find the angle subtending the lines, this topic should actually be in the Pre-Calculus forum. I'll wait until I know for sure before moving it.
 
Re: The angle between two line

MarkFL said:
If two vectors are normal (if I understand you to mean orthogonal or perpendicular) then their dot product will be zero. What you did was correct, you just need to solve for the angle using the inverse cosine function.

edit: Unless you are to use some other method to find the angle subtending the lines, this topic should actually be in the Pre-Calculus forum. I'll wait until I know for sure before moving it.
I solved it :) Thanks for the help!:)

Regards,
$$|\pi\rangle$$
 
Last edited:

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