How to Determine the Dimension of Span(1, cos(2x), cos²(x)) in C[-π, π]?

This means that one function can be written as a weighted sum of the other two functions. In this case, cos2x can be written as a linear combination of cosx and 1. In summary, the three given functions are not linearly independent because one of them can be expressed as a linear combination of the other two.
  • #1
Dustinsfl
2,281
5
C[-pi, pi]
Span(1, cos (2x), cos2 (x))

Doing the Wronskian here is pain so what other method would be more appropriate?
 
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  • #2
One of the functions is a linear combination of the other two, so the three functions can't be linearly independent.
 
  • #3
How can I go about identifying if one is?
 
  • #4
Use a trig identity for cos2x
 
  • #5
cos2x=2cos^2 x-1 but I don't see how that is a multiple of cos2x sine it doesn't = cos^2 x outright.
 
  • #6
Can cos2x can be written as a linear combination of cos2x and 1?
 
  • #7
I see now.
 
  • #8
Great :smile:
 
  • #9
Dustinsfl said:
cos2x=2cos^2 x-1 but I don't see how that is a multiple of cos2x sine it doesn't = cos^2 x outright.
I realize that you already figured this out, but if you look at what I said, I didn't say that one of the functions was a multiple of another. I said that one function was a linear combination of the other two.
 

FAQ: How to Determine the Dimension of Span(1, cos(2x), cos²(x)) in C[-π, π]?

What is a subspace in mathematics?

A subspace is a subset of a vector space that follows the same rules and operations as the vector space. It is closed under addition and scalar multiplication, and contains the zero vector.

How is the dimension of a subspace determined?

The dimension of a subspace is determined by the number of linearly independent vectors that span the subspace. This is also known as the number of basis vectors in the subspace.

Can a subspace have a dimension of zero?

Yes, a subspace can have a dimension of zero if it only contains the zero vector. This means that the subspace is trivial, or has no directionality.

What is the relationship between the dimension of a subspace and the dimension of its vector space?

The dimension of a subspace is always less than or equal to the dimension of its vector space. This is because a subspace is a subset of the vector space and cannot contain more dimensions than the vector space itself.

How can the dimension of a subspace be used in linear algebra?

The dimension of a subspace is important in linear algebra as it helps determine the number of free variables in a system of linear equations and the rank of a matrix. It is also used in finding the null space and column space of a matrix.

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