1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Linear algebra proof

  1. Oct 1, 2009 #1
    1. The problem statement, all variables and given/known data

    Prove or disprove: there exists a basis (p_0, p_1, p_2, p_3) of P_3 (F) such that one of the polynomials p_0, p_1, p_2, p_3 has degree 2.

    2. Relevant equations

    none really

    3. The attempt at a solution

    Is the following proof correct?


    Let p_0, p_1, p_2, p_3 be elements of P_3(F) s.t.

    p_o (x) = 1,
    p_1 (x) = x,
    p_2 (x) = x^2 + x^3,
    p_3(x) = x^3.

    None of the polynomials are degree 2 although (p_0,p_1,p_2,p_3) is clearly spanning P_3 (F) with dimP_3(F) = 4 and forms a basis. Hence proved.
  2. jcsd
  3. Oct 1, 2009 #2


    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    Looks good to me assuming the "one" in the statement of the problem should be "none".
  4. Oct 1, 2009 #3
    I'm not sure that stating that it clearly spans it will suffice even if it is obvious. If you think that this suffices for you class, you're fine.

    On the other hand, you could cook up a matrix that maps a degree three polynomial represented in the standard basis to it's representation in this basis pretty easily.
  5. Oct 1, 2009 #4
    Typo: the original statement is supposed to be "none of the polynomials has degree 2." Thanks for pointing that out, LCKurtz.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook