Prove that a triangle with lattice points cannot be equilateral

In summary, the conversation discusses the assumption of three points for a triangle with coordinates (a, c), (c, d), and (b, e), where a, b, c, d, and e are all integers. The conversation also mentions using the distance formula to set the distances between each point equal, but this leads to a contradiction and shows that the points do not form a triangle. The conversation also introduces the concept of a 2D lattice, where one of the lattice points can be set as (0,0) without losing generality. However, when using the formula for lattice points, it leads to a contradiction.
  • #1
JoeAllen
5
1
I assumed three points for a triangle P1 = (a, c), P2 = (c, d), P3 = (b, e)

and of course:
a, b, c, d, e∈Z
Using the distance formula between each of the points and setting them equal:
\sqrt { (b - a)^2 + (e - d)^2 } = \sqrt { (c - a)^2 + (d - d)^2 } = \sqrt { (b - c)^2 + (e - d)^2 }(e+d)2 = (c-a)2 - (b-a)2
(e+d)2 = (c-a)2 - (b-c)2

c2 - 2ac - b2 +2ab = -2ac + a2 - b2 + 2bc
c2 + 2ab = a2 + 2bc
c(c - 2b) = a(a - 2b)

Thus, for this to be true, a = c. But in this example, the distance between a and c would be 0. Thus, not a triangle and certainly not an equilateral triangle.

Where did I go wrong here? I'm bored waiting for Calculus II in the Fall and I'm going through Courant's Differential and Integral Calculus on my free time until then (Fall term probably starting in August/September, so I'm not worried if it takes a few months to get comfortable with Courant - Calculus I has been a breeze since I already knew most of the content before taking it).
 
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  • #2
As for 2D lattice we can make one of the lattice points is (0,0) without losing generality.
Say other points are ##(n_1,n_2),(m_1,m_2)##
[tex]n_1^2+n_2^2=A[/tex]
[tex]m_1^2+m_2^2=A[/tex]
[tex](n_1-m_1)^2+(n_2-m_2)^2=A[/tex]
where A is square of the side length. You will find contradiction in this set of formla.
 
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FAQ: Prove that a triangle with lattice points cannot be equilateral

1. What is a lattice point?

A lattice point is a point in the Cartesian coordinate system where both the x and y coordinates are integers. For example, the points (1, 2), (3, 4), and (0, 0) are all lattice points.

2. Why can't an equilateral triangle have all its vertices as lattice points?

An equilateral triangle has all sides of equal length, and the angles between the sides are all 60 degrees. When you calculate the distance between two lattice points, the resulting distance can only be expressed in a certain form, which does not fit the requirements of the equal length sides of an equilateral triangle when using integer coordinates.

3. What mathematical concepts are used to prove this statement?

The proof involves concepts from geometry, number theory, and the properties of distances between points in the Cartesian plane. Specifically, it uses the properties of the Pythagorean theorem and the fact that the distance formula between two lattice points yields a rational number, which cannot satisfy the conditions for an equilateral triangle.

4. Are there any exceptions to this rule?

No, there are no exceptions. The proof holds for any equilateral triangle, regardless of its size, as long as the vertices are required to be lattice points. The underlying mathematical principles ensure that such a configuration is impossible.

5. How can this concept be applied in other areas of mathematics?

This concept can be applied in various areas such as combinatorial geometry, number theory, and even in computer graphics where lattice points are often used to define shapes and structures. Understanding the limitations of lattice point configurations helps in exploring more complex geometric and algebraic structures.

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