Scalar product to prove triangle inequality?

In summary, the scalar product or dot product is a mathematical operation that takes two vectors as input and returns a scalar value by multiplying and adding their corresponding components. It can be used to prove the triangle inequality, which states that the sum of any two sides of a triangle must be greater than the third side. This is important because it provides a geometric interpretation of the dot product and helps understand the relationship between vectors and their lengths. The scalar product can also be used to prove other inequalities in geometry, but it is limited to Euclidean geometry and certain types of vectors.
  • #1
8emnero8
1
0

Homework Statement


From the inequality

|a.b| <= |a||b|

prove the triangle inequality:

|a+b| <= |a| + |b|

Homework Equations



a.b = |a|b| cos theta

The Attempt at a Solution



Making a triangle where side c = a+b. Don't know how to approach the question.

Thanks.
 
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  • #2
I may not be understanding your question, but it seems like you should start with the Pythagorean Identities.
 
  • #3
Also think about what values your trig function is between
 
  • #4
You should start by knowing |a+b|^2=(a+b).(a+b). Now expand the right side.
 

FAQ: Scalar product to prove triangle inequality?

1. What is the definition of scalar product?

The scalar product, also known as the dot product, is a mathematical operation that takes two vectors as input and returns a scalar value. It is calculated by multiplying the corresponding components of the two vectors and then adding them together.

2. How is scalar product used to prove triangle inequality?

The triangle inequality states that the sum of any two sides of a triangle must be greater than the third side. To prove this, the scalar product of the two sides can be compared to the scalar product of the third side and the sum of the other two sides. If the scalar product of the two sides is less than or equal to the scalar product of the third side, then the triangle inequality holds.

3. What is the importance of proving triangle inequality using scalar product?

Proving the triangle inequality using scalar product is important because it provides a geometric interpretation of the algebraic concept of the dot product. It also helps in understanding the relationship between vectors and their lengths or magnitudes.

4. Can scalar product be used to prove other inequalities in geometry?

Yes, scalar product can be used to prove other inequalities in geometry, such as the Cauchy-Schwarz inequality and the triangle inequality for higher dimensions. It is a useful tool in analyzing the properties of vectors and their relationships in geometric contexts.

5. Are there any limitations to using scalar product to prove triangle inequality?

One limitation of using scalar product to prove triangle inequality is that it only applies to Euclidean geometry, where the Pythagorean theorem holds true. It cannot be used in non-Euclidean geometries, such as spherical or hyperbolic geometries. Additionally, it may not hold true for all types of vectors, such as complex or infinite-dimensional vectors.

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