Finding the Matrix for d2/dx2 in V

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SUMMARY

The discussion focuses on constructing the matrix representation of the second derivative operator \( \frac{d^2}{dx^2} \) in the vector space \( V = \{ p \in \mathbb{R}[x] | \text{deg}(p) \leq 3 \} \) with the basis \( \{ 1, x, x^2, x^3 \} \). The correct matrix is a 4x4 matrix that transforms the coefficient vector of a polynomial into the coefficient vector of its second derivative. The accurate matrix representation is derived from applying the second derivative to each basis polynomial, resulting in the matrix: \[ \begin{bmatrix} 0 & 0 & 0 & 0 \\ 0 & 0 & 0 & 0 \\ 0 & 0 & 2 & 0 \\ 0 & 0 & 0 & 6 \end{bmatrix} \].

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Homework Statement



Let V = {p element of R[x] | deg(p) <=3} be the vector space of all polynomials of degree 3 or less.



b) Give the matrix for d2/dx2 in the basis {1,x,x^2, x^3} for V

Homework Equations





The Attempt at a Solution




[1 1 1 1
0 0 2 6]

i used the coefficients to get the first row, and then took the 2nd derivative and used the coefficients for the 2nd row. is this right?
 
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You have this all wrong. The matrix should be 4x4. The polynomial a+bx+cx^2+dx^3 corresponds to the column vector (a,b,c,d). Whatever the second derivative does to the polynomial, the matrix should do to the vector. E.g. x^3=(0,0,0,1), the second derivative is 3x^2=(0,0,3,0).
 

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