Animated Solution for Mathematics - Vector Algebra: Let α,β,γ be distinct real numbers. The points with position vectors αi^+βj^+γk^, βi^+γj^+αk^, γi^+αj^+βk^
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Visualized Solution
Visualizing the Points in 3D Space
Let the three given points be A(α,β,γ), B(β,γ,α), and C(γ,α,β).
These points are formed by cyclic permutations of the coordinates (α,β,γ).
We want to determine the geometric nature of the triangle formed by these three points.
The 3D Distance Formula
To find the nature of the triangle, we must calculate the lengths of its sides: AB, BC, and CA.
Recall the distance formula between two points (x1,y1,z1) and (x2,y2,z2) in 3D space:
d=(x2−x1)2+(y2−y1)2+(z2−z1)2
Setting up Distance AB
Let's substitute the coordinates of A(α,β,γ) and B(β,γ,α) into the distance formula.
AB=(β−α)2+(γ−β)2+(α−γ)2
This represents the distance between the first two vertices.
Simplifying the Expression for AB
Since (x−y)2=(y−x)2, we can rewrite the terms to keep them in a standard cyclic order:
AB=(α−β)2+(β−γ)2+(γ−α)2
This is a symmetric expression involving the squared differences of all three coordinates.
Setting up Distance BC
Now, let's find the length of the second side, BC, using the coordinates B(β,γ,α) and C(γ,α,β).
BC=(γ−β)2+(α−γ)2+(β−α)2
Comparing BC with AB
Let's rearrange the terms inside the square root of BC to match the order in AB:
BC=(α−β)2+(β−γ)2+(γ−α)2
Notice that the expression is mathematically identical to AB. Therefore, BC=AB.
Setting up Distance CA
Finally, let's calculate the length of the third side, CA, using the coordinates C(γ,α,β) and A(α,β,γ).
CA=(α−γ)2+(β−α)2+(γ−β)2
Comparing CA with AB and BC
Rearranging the terms for CA once again gives:
CA=(α−β)2+(β−γ)2+(γ−α)2
This is exactly the same expression as AB and BC. Thus, CA=AB=BC.
Establishing the Equilateral Nature
Since all three side lengths are equal:
AB=BC=CA
The triangle formed by these three points must be an equilateral triangle.
This elegant symmetry arises because the coordinates are cyclic permutations of each other.
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The Sigma Insight: Components of a Vector
Analyzing the Setup
Imagine you are standing in a vast 3D coordinate system. You are given three points, A(α,β,γ), B(β,γ,α), and C(γ,α,β).
At first glance, they might look like a random collection of variables. However, each point is simply a cyclic shift of the previous one. This is the hallmark of a highly symmetric system, and in geometry, symmetry is almost always a shortcut to elegance.
The Tool of Choice
To understand the nature of the triangle formed by these points, we need to determine the lengths of its sides. We reach for our most trusted tool in 3D geometry: the distance formula.
For any two points (x1,y1,z1) and (x2,y2,z2), the distance d is given by:
d=(x2−x1)2+(y2−y1)2+(z2−z1)2
This formula serves as our bridge between algebra and the physical shape of the triangle.
The Calculation
Let us calculate the length of side AB. Substituting our coordinates, we get:
AB=(β−α)2+(γ−β)2+(α−γ)2
Now, let us look at side BC. Using the coordinates of B and C, we find:
BC=(γ−β)2+(α−γ)2+(β−α)2
Notice that the terms inside the square root are identical to those in AB, just in a different order. Because addition is commutative, AB is exactly equal to BC.
Finally, we calculate CA:
CA=(α−γ)2+(β−α)2+(γ−β)2
Again, the terms are identical to the previous calculations.
The Conclusion
We have proven that AB=BC=CA. A triangle where all three sides are equal is, by definition, an equilateral triangle.
This result is not just a calculation; it is a testament to the power of symmetry. Even when the variables α,β,γ are unknown, the cyclic structure forces the points to maintain a perfect, balanced relationship.
You have just navigated a complex 3D problem by simply observing the underlying pattern. Keep this intuition sharp—it is exactly what you need to excel in JEE Advanced.