14-240/Tutorial-November4: Difference between revisions
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:First, let <math>f(x) \in W</math>. Then we can decompose <math>f(x)</math> since there is a <math>g(x) \in P_{n - 1}(R)</math> such that <math>f(x) = (x - a)g(x)</math>. From here, there are several approaches: |
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There are several approaches to this problem. |
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'''Approach 1: Use Isomorphisms''' |
'''Approach 1: Use Isomorphisms''' |
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:We that <math>W</math> is isomorphic to <math>P_{n - 1}</math>. Let <math>B = \{1, x, x^2, ..., x^{n - 1}\}</math> be the standard ordered basis of <math>P_{n - 1}(R)</math> and <math>S = \{x - a, (x - a)x, (x - a)x^2, ..., (x - a)x^{n - 1}\}</math> be a subset of W. Then there is a unique linear transformation <math>T:P_{n - 1} \to W</math> such that <math>T(f(x)) = (x - a)</math> where <math>f(x) \in P_{n - 1}</math>. Then show that <math>T</math> is one-to-one and onto. |
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'''Approach 2: Use the Rank-Nullity Theorem''' |
'''Approach 2: Use the Rank-Nullity Theorem''' |
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'''Approach 3: Find a Basis |
'''Approach 3: Find a Basis with the Decomposed Polynomial''' |
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'''Approach 4: Find a Basis without |
'''Approach 4: Find a Basis without the Decomposed Polynomial''' |
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Revision as of 16:21, 29 November 2014
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Boris
Question 26 on Page 57 in Homework 5
Let [math]\displaystyle{ a \in R }[/math] and [math]\displaystyle{ W = \{f \in P_n(R): f(a) = 0\} }[/math] be a subspace of [math]\displaystyle{ P_n(R) }[/math]. Find [math]\displaystyle{ dim(W) }[/math].
- First, let [math]\displaystyle{ f(x) \in W }[/math]. Then we can decompose [math]\displaystyle{ f(x) }[/math] since there is a [math]\displaystyle{ g(x) \in P_{n - 1}(R) }[/math] such that [math]\displaystyle{ f(x) = (x - a)g(x) }[/math]. From here, there are several approaches:
Approach 1: Use Isomorphisms
- We that [math]\displaystyle{ W }[/math] is isomorphic to [math]\displaystyle{ P_{n - 1} }[/math]. Let [math]\displaystyle{ B = \{1, x, x^2, ..., x^{n - 1}\} }[/math] be the standard ordered basis of [math]\displaystyle{ P_{n - 1}(R) }[/math] and [math]\displaystyle{ S = \{x - a, (x - a)x, (x - a)x^2, ..., (x - a)x^{n - 1}\} }[/math] be a subset of W. Then there is a unique linear transformation [math]\displaystyle{ T:P_{n - 1} \to W }[/math] such that [math]\displaystyle{ T(f(x)) = (x - a) }[/math] where [math]\displaystyle{ f(x) \in P_{n - 1} }[/math]. Then show that [math]\displaystyle{ T }[/math] is one-to-one and onto.
Approach 2: Use the Rank-Nullity Theorem
Approach 3: Find a Basis with the Decomposed Polynomial
Approach 4: Find a Basis without the Decomposed Polynomial
