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The angle between two lines

Petrus

Well-known member
Feb 21, 2013
739
Decide the angle between line \(\displaystyle x+2y-3=0\) and \(\displaystyle -3x+y+1=0\) we use ON-cordinate
progress
I know that their normalvector is \(\displaystyle (1,2)\) and \(\displaystyle (-3,1)\) but what shall I do next?
Is this correctly understand

Regards,
\(\displaystyle |\pi\rangle\)
 
Last edited:

MarkFL

Administrator
Staff member
Feb 24, 2012
13,775
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?
 

Petrus

Well-known member
Feb 21, 2013
739
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?
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,
\(\displaystyle |\pi\rangle\)
 

MarkFL

Administrator
Staff member
Feb 24, 2012
13,775
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.
 

Petrus

Well-known member
Feb 21, 2013
739
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.
I solved it :) Thanks for the help!:)

Regards,
\(\displaystyle |\pi\rangle\)
 
Last edited: