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The linear transformation \(L\) defined by \\[ L(p(x))=p^{\prime}(x)+p(0) \\] \(\operatorname{maps} P_{3}\) into \(P_{2} .\) Find the matrix representation of \(L\) with respect to the ordered bases \(\left[x^{2}, x, 1\right]\) and \([2,1-x] .\) For each of the following vectors \(p(x)\) in \(P_{3},\) find the coordinates of \(L(p(x))\) with respect to the ordered basis \([2,1-x]\) (a) \(x^{2}+2 x-3\) (b) \(x^{2}+1\) (c) \(3 x\) (d) \(4 x^{2}+2 x\)

Short Answer

Expert verified
The matrix representation of the linear transformation L with respect to the ordered bases \(\{x^2, x, 1\}\) and \(\{2, 1-x\}\) is: \[ A = \begin{bmatrix} 0 & 1/2 & 0 \\ -2 & -1/2 & 0 \\ \end{bmatrix} \] The coordinates of L(p(x)) with respect to the ordered basis \(\{2, 1-x\}\) are: (a) \(L(x^{2}+2 x-3)= \frac{1}{2}(2) + \frac{-7}{2}(1-x)\) (b) \(L(x^{2}+1)= \frac{1}{2}(2) + \frac{-3}{2}(1-x)\) (c) \(L(3x)= \frac{3}{2}(2) + \frac{-3}{2}(1-x)\) (d) \(L(4x^{2}+ 2x)= 1(2) + (-8)(1-x)\)

Step by step solution

01

Find images of the basis elements under L

Let's find the images of the basis elements \(x^2, x\) and \(1\) under L. We have: i) \(L(x^2) = (x^2)'+ x^2(0) = 2x\) ii) \(L(x)= (x)' + (x)(0) = 1\) iii) \(L(1) = (1)' + (1)(0)= 0\)
02

Express the images in terms of the basis \(\{2, 1-x\}\)

Now, let's express the images of the basis elements found in Step 1 in terms of the basis \(\{2, 1-x\}\): i) The image of \(x^2\) under L is \(2x\). To express it in terms of \(\{2, 1-x\}\), we need to find the coefficients \(a\) and \(b\) such that \(2x = a(2) + b(1-x)\). From this equation, we have: \(a=0\) and \(b=-2\). So, \(2x = 0(2) + (-2)(1-x)\) ii) The image of \(x\) under L is \(1\). To express it in terms of \(\{2, 1-x\}\), we need to find the coefficients \(a\) and \(b\) such that \(1 = a(2) + b(1-x)\). From this equation, we have: \(a=\frac{1}{2}\) and \(b=-\frac{1}{2}\). So, \(1 = \frac{1}{2}(2) + ( -\frac{1}{2})(1-x)\) iii) The image of \(1\) under L is \(0\). Since \(0\) is a trivial linear combination, we have: \(0 = 0(2) + 0(1-x)\)
03

Construct the matrix representation of L

Now, we will construct the matrix representation of L using the coefficients found in Step 2. The matrix A representing L with respect to the given bases is: \[ A = \begin{bmatrix} 0 & 1/2 & 0 \\ -2 & -1/2 & 0 \\ \end{bmatrix} \]
04

Compute L(p(x)) for the given input polynomials

Now, we are ready to find the transformed polynomials for the given input polynomials in terms of the basis \(\{2, 1-x\}\): (a) \(L(x^{2}+2x-3)\): Reach the final answer using the matrix representation on \(p(x)= x^{2}+2x−3\) A[p(x)] = \[ \begin{bmatrix}0 & 1/2 & 0 \\ -2 & -1/2 & 0 \\\end{bmatrix} \begin{bmatrix}1 \\ 2 \\ -3 \\\end{bmatrix} = \begin{bmatrix}\frac{1}{2} \\ -\frac{7}{2} \\ \end{bmatrix}\] Therefore, \(L(x^{2}+2 x-3)= \frac{1}{2}(2) + \frac{-7}{2}(1-x)\) (b) \(L(x^{2}+1)\): Reach the final answer using the matrix representation on \(p(x)= x^{2}+1\) A[p(x)] = \[ \begin{bmatrix}0 & 1/2 & 0 \\ -2 & -1/2 & 0 \\\end{bmatrix} \begin{bmatrix}1 \\ 0 \\ 1 \\\end{bmatrix} = \begin{bmatrix}\frac{1}{2} \\ -\frac{3}{2} \\ \end{bmatrix}\] Therefore, \(L(x^{2}+1)= \frac{1}{2}(2) + \frac{-3}{2}(1-x)\) (c) \(L(3x)\): Reach the final answer using the matrix representation on \(p(x)= 3x\) A[p(x)] = \[ \begin{bmatrix}0 & 1/2 & 0 \\ -2 & -1/2 & 0 \\\end{bmatrix} \begin{bmatrix}0 \\ 3 \\ 0 \\\end{bmatrix} = \begin{bmatrix}\frac{3}{2} \\ -\frac{3}{2} \\ \end{bmatrix}\] Therefore, \(L(3x)= \frac{3}{2}(2) + \frac{-3}{2}(1-x)\) (d) \(L(4x^{2} + 2x)\): Reach the final answer using the matrix representation on \(p(x)= 4x^{2}+2x\) A[p(x)] = \[ \begin{bmatrix}0 & 1/2 & 0 \\ -2 & -1/2 & 0 \\\end{bmatrix} \begin{bmatrix}4 \\ 2 \\ 0 \\\end{bmatrix} = \begin{bmatrix}1 \\ -8 \\ \end{bmatrix}\] Therefore, \(L(4x^{2}+ 2x)= 1(2) + (-8)(1-x)\)

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Most popular questions from this chapter

Let \(L\) be the linear operator mapping \(\mathbb{R}^{3}\) into \(\mathbb{R}^{3}\) defined by \(L(\mathbf{x})=A \mathbf{x},\) where $$A=\left(\begin{array}{rrr} 3 & -1 & -2 \\ 2 & 0 & -2 \\ 2 & -1 & -1 \end{array}\right)$$ and let $$\mathbf{v}_{1}=\left(\begin{array}{l} 1 \\ 1 \\ 1 \end{array}\right), \quad \mathbf{v}_{2}=\left(\begin{array}{l} 1 \\ 2 \\ 0 \end{array}\right), \quad \mathbf{v}_{3}=\left(\begin{array}{r} 0 \\ -2 \\ 1 \end{array}\right)$$ Find the transition matrix \(V\) corresponding to a change of basis from \(\left\\{\mathbf{v}_{1}, \mathbf{v}_{2}, \mathbf{v}_{3}\right\\}\) to \(\left\\{\mathbf{e}_{1}, \mathbf{e}_{2}, \mathbf{e}_{3}\right\\},\) and use it to determine the matrix \(B\) representing \(L\) with respect to \(\left\\{\mathbf{v}_{1}, \mathbf{v}_{2}, \mathbf{v}_{3}\right\\}\)

Let \\[ R=\left(\begin{array}{lllll} 0 & 0 & 1 & 1 & 0 \\ 0 & 1 & 1 & 0 & 0 \\ 1 & 1 & 1 & 1 & 1 \end{array}\right) \\] The column vectors of \(R\) represent the homogeneous coordinates of points in the plane. (a) Draw the figure whose vertices correspond to the column vectors of \(R .\) What type of figure is it? (b) For each of the following choices of \(A\), sketch the graph of the figure represented by \(A R\) and describe geometrically the effect of the linear transformation: $$\text { (i) } A=\left(\begin{array}{ccc} \frac{1}{2} & 0 & 0 \\ 0 & \frac{1}{2} & 0 \\ 0 & 0 & 1 \end{array}\right)$$ $$\text { (ii) } A=\left(\begin{array}{rrr} \frac{1}{\sqrt{2}} & \frac{1}{\sqrt{2}} & 0 \\ -\frac{1}{\sqrt{2}} & \frac{1}{\sqrt{2}} & 0 \\ 0 & 0 & 1 \end{array}\right)$$ $$\text { (iii) } A=\left(\begin{array}{rrr} 1 & 0 & 2 \\ 0 & 1 & -3 \\ 0 & 0 & 1 \end{array}\right)$$

Let \(V\) and \(W\) be vector spaces with ordered bases \(E\) and \(F,\) respectively. If \(L: V \rightarrow W\) is a linear transformation and \(A\) is the matrix representing \(L\) relative to \(E\) and \(F,\) show that (a) \(\mathbf{v} \in \operatorname{ker}(L)\) if and only if \([\mathbf{v}]_{E} \in N(A)\) (b) \(\mathbf{w} \in L(V)\) if and only if \([\mathbf{w}]_{F}\) is in the column space of \(A\)

Let \(L\) be the linear transformation on \(\mathbb{R}^{3}\) defined by $$L(\mathbf{x})=\left(\begin{array}{l} 2 x_{1}-x_{2}-x_{3} \\ 2 x_{2}-x_{1}-x_{3} \\ 2 x_{3}-x_{1}-x_{2} \end{array}\right)$$ and let \(A\) be the standard matrix representation of \(L(\text { see Exercise } 4 \text { of Section } 2) .\) If \(\mathbf{u}_{1}=\) \((1,1,0)^{T}, \mathbf{u}_{2}=(1,0,1)^{T},\) and \(\mathbf{u}_{3}=(0,1,1)^{T}\) then \(\left\\{\mathbf{u}_{1}, \mathbf{u}_{2}, \mathbf{u}_{3}\right\\}\) is an ordered basis for \(\mathbb{R}^{3}\) and \(U=\) \(\left(\mathbf{u}_{1}, \mathbf{u}_{2}, \mathbf{u}_{3}\right)\) is the transition matrix corresponding to a change of basis from \(\left\\{\mathbf{u}_{1}, \mathbf{u}_{2}, \mathbf{u}_{3}\right\\}\) to the standard basis \(\left\\{\mathbf{e}_{1}, \mathbf{e}_{2}, \mathbf{e}_{3}\right\\} .\) Determine the matrix \(B\) representing \(L\) with respect to the basis \(\left\\{\mathbf{u}_{1}, \mathbf{u}_{2}, \mathbf{u}_{3}\right\\}\) by calculating \(U^{-1} A U\).

Use mathematical induction to prove that if \(L\) is a linear transformation from \(V\) to \(W\), then \\[ \begin{array}{l} L\left(\alpha_{1} \mathbf{v}_{1}+\alpha_{2} \mathbf{v}_{2}+\cdots+\alpha_{n} \mathbf{v}_{n}\right) \\ \quad=\alpha_{1} L\left(\mathbf{v}_{1}\right)+\alpha_{2} L\left(\mathbf{v}_{2}\right)+\cdots+\alpha_{n} L\left(\mathbf{v}_{n}\right) \end{array} \\]

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