Math Is Fun Forum

pari_alf

Member

Registered: 2013-12-01

Posts: 85

direction of line segments

Hi,

  I have three Points A(2,3) , B(3,1), C(9,3).
so i would have 2 line segments ab and bc.
I wanted to get the direction of line segment.
How could i get that.

bobbym

bumpkin

From: Bumpkinland

Registered: 2009-04-12

Posts: 109,606

Re: direction of line segments

Hi;

Which line segment? AC?

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If it ain't broke, fix it until it is.
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pari_alf

Member

Registered: 2013-12-01

Posts: 85

Re: direction of line segments

yes, what i wanna do is.. if angel of segment ab is same as angle of bc
that meant points a ,b ,c are in the same direction.

then delete point b.. so we will consider line from point A to C.
so finally we should have a line AC with direction.

In other words we can say that point A , B , C are coplanar.

so to get the direction of segments, we need to get angle.

to get angle, i used this method

theta = acos ( (u.v) / |u| * |v| )

but this give angle of point with origin.

i don't need in that way.

Last edited by pari_alf (2013-12-01 01:22:10)

Bob

Administrator

Registered: 2010-06-20

Posts: 10,643

Re: direction of line segments

hi pari_alf

Welcome to the forum.

You can use that formula but you need vectors that give the directions of the lines; eg

But, if all you want is to see if the points are co-linear, you could just work out the gradient of AB and the gradient of BC, to see if they are the same.

Bob

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Children are not defined by school ...........The Fonz
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pari_alf

Member

Registered: 2013-12-01

Posts: 85

Re: direction of line segments

hi pari_alf

Welcome to the forum.

You can use that formula but you need vectors that give the directions of the lines; eg

But, if all you want is to see if the points are co-linear, you could just work out the gradient of AB and the gradient of BC, to see if they are the same.

Bob

Thanks bob