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#1 2008-11-25 18:07:50

Rex Noda

angle and straight angle

The definition of an angle is a distance between two non-collinear rays with common endpoint called vertex.

The word non-collinear contradicts the definition of a straight angle whose measurement is 180 degrees.

How do you explain it?

A straight angle is composed two collinear rays whose measurement is 180 degrees but the the definition of an angle states the "non-collinear" rays.

#2 2008-11-25 18:31:21

Registered: 2005-06-28
Posts: 25,914

Re: angle and straight angle

collinear represents two lines lying on the same straight line.

First and foremost, please understand the difference between a ray, a line and a line segment.

    |------------------------------------>   = Ray

    <------------------------------------>  = Straight line

    |--------------------------------------|  = Line segement

    <---------------||--------------------> = Two rays whose measurement is 180 degress but no vertex is said to exist, just the meeting point of the two starting points of the rays. If the two rays form an angle other than 180 degrees or 360 degress, there would be a vertex.

PS:- I have tried to explain from whatever I learnt in my early school days and that was very long back. Please correct me if I am wrong, Mods/Members.

It is no good to try to stop knowledge from going forward. Ignorance is never better than knowledge - Enrico Fermi. 

Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.


#3 2009-09-14 04:20:33


Re: angle and straight angle

two rays whose measurement is 180 degrees does not mean that they are collided or connected.  Therefore, there is no vertex exists.  I am looking for an answer for the definition of angle and straight angle.  Thanks!

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