Can Lagrange's Identity Help Prove Coplanarity of Vectors a, b, c, and d?

Sammy discuss the problem of showing that a,b,c,d are coplanar if (a \times b) \times (c \times d) = 0. BiP suggests using Lagrange's identity, but Sammy points out that the statement is not true because if (a \times b) = 0, then c and d can be anything.
  • #1
Bipolarity
776
2

Homework Statement


If [itex] (a \times b) \times (c \times d) = 0 [/itex], show that a,b,c,d are coplanar.


Homework Equations





The Attempt at a Solution


I have done the converse of this problem, but am having trouble on how to do this. Can we perhaps use Lagrange's identity. How can I start?

BiP
 
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  • #2
Bipolarity said:

Homework Statement


If [itex] (a \times b) \times (c \times d) = 0 [/itex], show that a,b,c,d are coplanar.

Homework Equations



The Attempt at a Solution


I have done the converse of this problem, but am having trouble on how to do this. Can we perhaps use Lagrange's identity. How can I start?

BiP
It's not true.

If [itex](a \times b)=0\,,[/itex] the c & d can be anything.
 
  • #3
SammyS said:
It's not true.

If [itex](a \times b)=0\,,[/itex] the c & d can be anything.

Thanks Sammy!

BiP
 

Related to Can Lagrange's Identity Help Prove Coplanarity of Vectors a, b, c, and d?

1. What is a vector?

A vector is a mathematical object that has both magnitude (or size) and direction. It can be represented by an arrow, with the length of the arrow representing the magnitude and the direction it points in representing the direction.

2. What is a vector proof?

A vector proof is a mathematical argument or demonstration that uses the properties and operations of vectors to show that a certain statement or equation is true.

3. Why are vector proofs important?

Vector proofs are important because they help us understand and apply the principles of vectors in various mathematical and scientific fields, such as physics and engineering. They also help us to develop problem-solving skills and logical thinking.

4. How do you write a vector proof?

To write a vector proof, you first need to clearly state the statement or equation you want to prove. Then, you can use the properties and operations of vectors, such as addition, subtraction, and scalar multiplication, to manipulate the given information and arrive at the desired conclusion.

5. What are common mistakes to avoid in a vector proof?

Common mistakes to avoid in a vector proof include incorrect use of vector operations, not clearly stating the given information and desired conclusion, and not providing enough justification or explanation for each step of the proof. It is also important to check for errors and ensure that the proof is logically sound and follows the rules of vector algebra.

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