Letter Names for Triangles
Date: 05/16/2000 at 13:44:47 From: Bob Newman Subject: Letter Names for Triangles Hi, When a triangle is named by the letters of its vertices, why are the letters in the order they are? Could they be in any order? (For example: ABC, ACB, CBA, etc.) I'm comparing triangles and rectangles to their letter names on the answer sheet, and I don't see why they are named the way they are. Can you help me? Thanks, Bob Newman
Date: 05/16/2000 at 16:55:58 From: Doctor Rick Subject: Re: Letter Names for Triangles Hi, Bob. Sometimes the order matters, but often it doesn't. It depends what the question is. One time when it matters is when you want to name the triangle that is congruent or similar to a particular named triangle. For instance, if triangle BAC is similar to triangle DEF, A /\ / \ E / \ /\ / \ / \ /____________\ /______\ B C D F it means that angle B is congruent to angle D, angle A is congruent to angle E, and angle C is congruent to angle F. That's not the same as saying that triangle ABC is similar to triangle DEF. In that case, angle A is congruent to angle D, angle B is congruent to angle E, and angle C is congruent to angle F. The matching angles in the two triangles must be named in the same order. When you name a rectangle (or any figure with more than 3 vertices), it's always important that you name the vertices in order either clockwise or counterclockwise around the figure. If I referred to this rectangle, ABCD, A ____B | | | | | | |____| D C as rectangle ABDC, that would be wrong: it would describe this figure instead (which is not a rectangle): A____B \ / \/ /\ /__\ D C You can't make this mistake with a triangle, because no matter in which order you put the vertices, they will go either clockwise or counterclockwise around the triangle. But I can imagine times when your teacher might want you to name the vertices in clockwise order, or else in counterclockwise order. You'd have to ask your teacher. - Doctor Rick, The Math Forum http://mathforum.org/dr.math/
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