Angles: Acute, Right, Obtuse, Reflex

Date: 06/06/2001 at 23:12:07
From: vosia
Subject: Math angles

How can I remember what the names of angles mean? For example, acute 
angle, right angle.

Date: 06/07/2001 at 23:17:19
From: Doctor Peterson
Subject: Re: Math angles

Hi, Vosia.

Here they are:

      \              |              /
       \             |             /
        \ A          |A           / A
         +-------    +-------    +-------
        obtuse        right       acute   angle
         >90           90          <90    degrees

We can start with the right angle: it's called that because it "stands 
upright." Just remember it's an "upright angle."

Next, the acute angle. That word comes from a word that means "sharp"; 
a sharp pencil or a sharp knife will look like this. An acute pain is 
a sharp pain. Acupuncture uses sharp needles. And, if all else fails, 
you can remember that an aCUTe angle is one that can CUT you!

Finally, we don't use the word "obtuse" so much apart from angles; but 
it means "dull." If a person isn't very "sharp" (doesn't have an acute 
intelligence), he may be called "obtuse." If that doesn't stick in 
your mind, just remember that if it isn't right or acute, it's obtuse.

Perhaps I should mention a fourth kind of angle, the reflex angle. 
This can look like any of the others, but we're measuring it around 
the back; if what we're measuring is on top, it will look like this:

        A
         +-------
        /
       /
      /
         reflex
         >180 degrees

"Reflex" means "bent back"; it's like an elbow that bent too far, 
which would probably hurt a lot.

I hope this makes the names memorable; if you need any more help, and 
especially if your problem was not with the names but something else, 
please write back.

- Doctor Peterson, The Math Forum
  http://mathforum.org/dr.math/