Matrix representation relative to bases

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The discussion focuses on the correct matrix representation for a linear transformation T from a 3-D space to a 2-D space. It highlights that the transformation should be represented by a 2x3 matrix, with the number of columns matching the dimension of the source space and the number of rows matching the dimension of the target space. The participants clarify that each column of the matrix is determined by applying T to the basis vectors of the source space. Specifically, the transformation of the vector representing a constant polynomial results in a 2-D vector, illustrating the mapping from a higher to a lower dimension. Understanding the definition of T is crucial for grasping how the transformation operates mathematically.
Robb
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Homework Statement



Please see attached file. I'm not quite sure if I'm on the right track here. I think the basis for F is throwing me off as well as T(f). Please advise. Thanks!

Homework Equations

The Attempt at a Solution

 

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Ok I can see the logic that led you through this attempt but it's not quite correct. First off you have a 3x3 matrix for a transformation that goes from a 3-D space to a 2-D one. This is already troublesome. You want your number of columns to be equal to ##\dim{U}## and the number of rows to be equal to the dimension of your target space i.e. ##\dim{V}##. So in this case you want a 2x3 matrix.

As for the entries of the matrix, each column is directed by letting ##T## act on a basis vector from ##U##. For example, if we have the vector ##
\begin{pmatrix} 1\\ 0\\ 0
\end{pmatrix}## which represents a constant polynomial equal to ##1##, then ##T(
\begin{pmatrix} 1\\ 0\\ 0
\end{pmatrix})## gives us ##
\begin{pmatrix}
1\\
0
\end{pmatrix}## as represented by the basis ##F## in the space ##V##.
 
GwtBc said:
Ok I can see the logic that led you through this attempt but it's not quite correct. First off you have a 3x3 matrix for a transformation that goes from a 3-D space to a 2-D one. This is already troublesome. You want your number of columns to be equal to ##\dim{U}## and the number of rows to be equal to the dimension of your target space i.e. ##\dim{V}##. So in this case you want a 2x3 matrix.

As for the entries of the matrix, each column is directed by letting ##T## act on a basis vector from ##U##. For example, if we have the vector ##
\begin{pmatrix} 1\\ 0\\ 0
\end{pmatrix}## which represents a constant polynomial equal to ##1##, then ##T(
\begin{pmatrix} 1\\ 0\\ 0
\end{pmatrix})## gives us ##
\begin{pmatrix}
1\\
0
\end{pmatrix}## as represented by the basis ##F## in the space ##V##.

Ok, I guess I'm unsure of
##T(
\begin{pmatrix} 1\\ 0\\ 0
\end{pmatrix})## gives us ##
\begin{pmatrix}
1\\
0

How does this go from a 3x1 to a 2x1 vector. I'm not seeing the math behind it.
 
Robb said:
Ok, I guess I'm unsure of
##T(
\begin{pmatrix} 1\\ 0\\ 0
\end{pmatrix})## gives us ##
\begin{pmatrix}
1\\
0

How does this go from a 3x1 to a 2x1 vector. I'm not seeing the math behind it.
That's just how ##T## is defined. It's a transformation that takes a vector from a 3-D space to a 2-D space. In terms of the actual calculation, you let ##T## operate on a basis vectors of E (which is a basis for ##U##). So the first one is ##\begin{pmatrix} 1\\ 0\\0 \end{pmatrix}## which represents the polynomial ##f(t) = 1##. Then ##f(3) = 1## and ##f'(3)=0##, which if represented by the basis vectors of ##F## (which is a basis for ##V##) is ##\begin{pmatrix} 1\\ 0 \end{pmatrix}##
 
Question: A clock's minute hand has length 4 and its hour hand has length 3. What is the distance between the tips at the moment when it is increasing most rapidly?(Putnam Exam Question) Answer: Making assumption that both the hands moves at constant angular velocities, the answer is ## \sqrt{7} .## But don't you think this assumption is somewhat doubtful and wrong?

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