Triangle With No Area

Geometry Level 1

True or False?

A triangle can have zero area.

False True

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5 solutions

Aareyan Manzoor
Jan 9, 2016

We know the formula for the area of triangle is 1 2 a b sin C \dfrac{1}{2}ab\sin C . For the area to be zero we need, by the Zero Product Property , a = 0 a=0 or b = 0 b=0 or sin C = 0 \sin C=0 . We know that the sides of a triangle are always positive. so a , b ∉ { 0 } 2 a,b\not\in\{0\}^2 . We are left with sin C = 0 C = 0 , π ( range of triangle angles as the sum is π ) \sin C=0 ~\Rightarrow~ C=0, ~\pi~ (\text{range of triangle angles as the sum is}~\pi) As a triangle cannot have 0° or 180° , we see that none of our solutions are possible, and conclude that a triangle always has a positive area.

But area-0 means its vertices are collinear! isin't that so?

sakshi rathore - 5 years, 5 months ago

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yeah but that isnt a triangle anymore!

Prince Loomba - 5 years, 5 months ago

What about a degenerate triangle?

Michael Fuller - 5 years, 5 months ago

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degenarate triangles are like analytical continuation of triangles. i.e defined in unit circle.

Aareyan Manzoor - 5 years, 5 months ago

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That's not what analytic continuation is.

Jake Lai - 5 years, 5 months ago

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@Jake Lai I know that! The word "like" is to say that it is something like the analytical continuation: defined for unit circle but not defined in "plain geometry".

Aareyan Manzoor - 5 years, 5 months ago

That is not helpful, nor does it explain anything. Unfortunately, it makes you sound stuck up and pompous instead.

Insetad, you should have said "A degenerate triangle is not considered a triangle. As a similar example, the triangle is not considered a degenerate pyramid with no height".

Calvin Lin Staff - 5 years, 4 months ago

0 cm exists, then a regular triangle can have all sides, 0 cm.

So, (0*0)/2=0.

Thus, a triangle can have zero areas.

. . - 1 month, 3 weeks ago

What about a Sierpinski Triangle?

It is possible!

alex wang - 4 years, 11 months ago

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That is not a triangle even though there's the word triangle in the name.

Calvin Lin Staff - 4 years, 11 months ago

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But it is connected through 3 points so why is it not a triangle?

alex wang - 4 years, 11 months ago
Jake Lai
Jan 14, 2016

The triangle inequality says that, for a triangle with sides a, b, and c, a+b > c.

If we let the zero side be a, then b = c; however, by the inequality we have b > c.

Thus, we have a contradiction, and our initial assumption is false.

No it does not: "the sum of the lengths of any two sides must be greater than or equal to the length of the remaining side." https://en.m.wikipedia.org/wiki/Triangle_inequality

How could the makers of this section miss the "or equal"? Degenerate triangles are still triangles, otherwise they would not be called triangles...

Marcus Appelros - 3 years, 7 months ago

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Marcus, this works. Note that a degenerate triangle has actually 0 area. That's because it's basically a segment, with a point marked inside it. It's not a polygon, it doesn't have height, therefore you can't define an area to it.

Mihaly Hanics - 3 years, 6 months ago
Harsh Harsh
Jul 11, 2020

It is not possible that a bounded polygon doesn't enclosed region in plane it is possible when figure is not bounded polygon

Joe Peters
Jan 5, 2018

The two legs of a triangle cannot both equal 0 in length, so the hypotenuse cannot equal 0. Therefore, no two sides can equal 0. A=0.5bh. Also, if a figure had zero area, wouldn't it just be a point? To extend on the above, no side or angle can have a negative length or measure, so we cannot have two opposites in a triangle. (i.e.: a whole number and its opposite, such as 1 and -1.). Consequently, no combination of sides or angles could cancel each other out. link text

Also..... point OR A LINE.(A line has 0 area.)

Elisa Abarquez - 3 years, 2 months ago
Harshit Mittal
Jan 18, 2016

If The Triangle Can Have Zero Area Than It Is A Point.

You do have a point ;)

Jayden Binno - 4 years, 2 months ago

Although the triangle have zero area but such a triangle exists ! why we reject it because it has zero area. how can we find sin(0) and sin(90) if such a triangle doesn't exist. take into account , the most important mathematical fact : that zero is a number ! and it exists ! it is conluded that : " If The Triangle Can Have Zero Area Than It Is A Point. or a line ". but if we suppose that a trriangle with sides 3,4,5 its area= 6 ........................(A). of course the above triangle is just a collection of points or lines , suppose the sum of these points or lines is 100 billions or what ever , the sum of their areas = zero ! which contradicts the above equation (A) am i right or not !

Aziz Alasha - 4 years, 8 months ago

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