Set of polynomial forming a basis for $P_2$












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$begingroup$


I was asked to find which of these sets formed a basis for $P_2$



I got the answer wrong and cannot answer again, but its going to drive me crazy if i don't understand what I did wrong.



So...




  1. $p_1 = 1+x, p_2 = 3x+x^2,p_3 = 1+4x+x^2$


  2. $p_1 = 1, p_2 = 1-5x,p_3 = x, p_4 = x^2$


  3. $p_1 = 1+3x+5x^2, p_2 = 3+x$



I expanded all of them in the form $a(p_1) + b(p_2) + c(p_3)....$



After which I put them into matrix form and calculated the determinant.



For 1. The determinant was 0 and thus not linearly independent so it does not span $P_2$



For 2. The determinant was -1 and thus linearly independent so it does span $P_2$



For 3. I got a 2 x 3 matrix for which I was not sure how to proceed as I could not calculate the determinant.










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$endgroup$












  • $begingroup$
    How did you compute the determinants of non-square matrices?
    $endgroup$
    – amd
    Nov 28 '18 at 21:30












  • $begingroup$
    HINT: How many elements must there be in a basis for $P_2$?
    $endgroup$
    – amd
    Nov 28 '18 at 21:30


















0












$begingroup$


I was asked to find which of these sets formed a basis for $P_2$



I got the answer wrong and cannot answer again, but its going to drive me crazy if i don't understand what I did wrong.



So...




  1. $p_1 = 1+x, p_2 = 3x+x^2,p_3 = 1+4x+x^2$


  2. $p_1 = 1, p_2 = 1-5x,p_3 = x, p_4 = x^2$


  3. $p_1 = 1+3x+5x^2, p_2 = 3+x$



I expanded all of them in the form $a(p_1) + b(p_2) + c(p_3)....$



After which I put them into matrix form and calculated the determinant.



For 1. The determinant was 0 and thus not linearly independent so it does not span $P_2$



For 2. The determinant was -1 and thus linearly independent so it does span $P_2$



For 3. I got a 2 x 3 matrix for which I was not sure how to proceed as I could not calculate the determinant.










share|cite|improve this question









$endgroup$












  • $begingroup$
    How did you compute the determinants of non-square matrices?
    $endgroup$
    – amd
    Nov 28 '18 at 21:30












  • $begingroup$
    HINT: How many elements must there be in a basis for $P_2$?
    $endgroup$
    – amd
    Nov 28 '18 at 21:30
















0












0








0





$begingroup$


I was asked to find which of these sets formed a basis for $P_2$



I got the answer wrong and cannot answer again, but its going to drive me crazy if i don't understand what I did wrong.



So...




  1. $p_1 = 1+x, p_2 = 3x+x^2,p_3 = 1+4x+x^2$


  2. $p_1 = 1, p_2 = 1-5x,p_3 = x, p_4 = x^2$


  3. $p_1 = 1+3x+5x^2, p_2 = 3+x$



I expanded all of them in the form $a(p_1) + b(p_2) + c(p_3)....$



After which I put them into matrix form and calculated the determinant.



For 1. The determinant was 0 and thus not linearly independent so it does not span $P_2$



For 2. The determinant was -1 and thus linearly independent so it does span $P_2$



For 3. I got a 2 x 3 matrix for which I was not sure how to proceed as I could not calculate the determinant.










share|cite|improve this question









$endgroup$




I was asked to find which of these sets formed a basis for $P_2$



I got the answer wrong and cannot answer again, but its going to drive me crazy if i don't understand what I did wrong.



So...




  1. $p_1 = 1+x, p_2 = 3x+x^2,p_3 = 1+4x+x^2$


  2. $p_1 = 1, p_2 = 1-5x,p_3 = x, p_4 = x^2$


  3. $p_1 = 1+3x+5x^2, p_2 = 3+x$



I expanded all of them in the form $a(p_1) + b(p_2) + c(p_3)....$



After which I put them into matrix form and calculated the determinant.



For 1. The determinant was 0 and thus not linearly independent so it does not span $P_2$



For 2. The determinant was -1 and thus linearly independent so it does span $P_2$



For 3. I got a 2 x 3 matrix for which I was not sure how to proceed as I could not calculate the determinant.







linear-algebra






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share|cite|improve this question











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asked Nov 28 '18 at 21:24









ForextraderForextrader

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677












  • $begingroup$
    How did you compute the determinants of non-square matrices?
    $endgroup$
    – amd
    Nov 28 '18 at 21:30












  • $begingroup$
    HINT: How many elements must there be in a basis for $P_2$?
    $endgroup$
    – amd
    Nov 28 '18 at 21:30




















  • $begingroup$
    How did you compute the determinants of non-square matrices?
    $endgroup$
    – amd
    Nov 28 '18 at 21:30












  • $begingroup$
    HINT: How many elements must there be in a basis for $P_2$?
    $endgroup$
    – amd
    Nov 28 '18 at 21:30


















$begingroup$
How did you compute the determinants of non-square matrices?
$endgroup$
– amd
Nov 28 '18 at 21:30






$begingroup$
How did you compute the determinants of non-square matrices?
$endgroup$
– amd
Nov 28 '18 at 21:30














$begingroup$
HINT: How many elements must there be in a basis for $P_2$?
$endgroup$
– amd
Nov 28 '18 at 21:30






$begingroup$
HINT: How many elements must there be in a basis for $P_2$?
$endgroup$
– amd
Nov 28 '18 at 21:30












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