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Nilpotent Operator

  • Thread starter johnson123
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  • #1
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1. Homework Statement

If T is a nilpotent transformation from V -> V, V - finite dimensional vector space.

show that [tex]a_{0}+a_{1}T+\cdots+a_{k}T^{k}[/tex] is invertible. [tex]a_{0}[/tex] nonzero.

Im having trouble finding the inverse, I know for 1+T+[tex]\cdots[/tex]+T[tex]^{m-1}[/tex]

the inverse is (1-T),where T[tex]^{m}[/tex]=0. I also tried [tex]a_{0}^{-1}T^{m-1}[/tex]
but this gives me [tex]T^{m-1}[/tex]
 
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Answers and Replies

  • #2
Dick
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Write that as -a0*I=a_1*T+a_2*T^2+...+a_k*T^k. Is that enough of a hint? If not notice the right side has a common factor.
 
  • #3
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I see that it shows T to be invertible but how does it show that the original polynomial

is invertible?
 
  • #4
Dick
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I see that it shows T to be invertible but how does it show that the original polynomial

is invertible?
Good point. I was solving the wrong problem.
 
  • #5
Hurkyl
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I also tried [tex]a_{0}^{-1}T^{k-1}[/tex]
but this gives me [tex]T^{k-1}[/tex]
Okay, so you figured to annihilate all of the terms of your polynomial except the T^{k-1} term. What else can you annihilate?
 
  • #6
Dick
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I think you are going to have a hard time expressing an answer in closed form in terms of the a_i's. But think of it this way. If P is your polynomial, then P=a0+Q where Q is the rest of the terms. Can you show Q is nilpotent? Does that suggest how to invert a0+Q?
 

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