What is the basis for the subspace W spanned by {sin^2(x), cos^2(x), cos2x}?

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Discussion Overview

The discussion centers on the subspace W of C[0,1] spanned by the set S={sin^2(x), cos^2(x), cos2x}. Participants explore the linear independence of the functions in S and seek to identify a basis for W.

Discussion Character

  • Technical explanation
  • Mathematical reasoning
  • Homework-related

Main Points Raised

  • One participant claims that S is not a basis for W because it is not linearly independent.
  • Another suggests using trigonometric identities to express one function in terms of the others to identify which function is superfluous.
  • A later reply emphasizes the need to show which functions are superfluous to establish a basis.
  • Another participant notes that since the functions span a space of fewer than three dimensions, the dimension must be 0, 1, or 2, and concludes that 0 or 1 is nonsensical, implying that two functions must be independent.

Areas of Agreement / Disagreement

Participants generally agree that the functions in S are not linearly independent and that a basis for W can be found, but there is no consensus on the specific basis or the method to derive it.

Contextual Notes

The discussion does not resolve the specific mathematical steps needed to identify the basis or clarify the dependencies among the functions in S.

physicsss
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I'm stumped by this problem:

let W be the subspace of C[0,1] spanned by S={sin^2(x),cos^2(x),cos2x}

a) explain why S is not a basis for W

it's because S not linearly independent

b) find a basis for W

please help me with this one...

TIA.
 
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physicsss said:
I'm stumped by this problem:

let W be the subspace of C[0,1] spanned by S={sin^2(x),cos^2(x),cos2x}

a) explain why S is not a basis for W

it's because S not linearly independent

b) find a basis for W

please help me with this one...

TIA.
This one is easy think about trig identities and try to express one function in terms of the others. See which function is superfluous.
 
show each one is superfluous.
 
Oh..sorry for the confusion. I just needed help with b). I already know how to do a).
 
and they answered b for you. they span a space of fewer then 3 dimensions, so it's 0,1 or 2, but obviously 0 or 1 is nonsense so you just need to find two of them that aer independent. as mathwonk says any two will do.
 

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