Solving Eigenvector Problems: A+B and AB with Corresponding Eigenvalues

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SUMMARY

The discussion focuses on demonstrating that if v is an eigenvector of matrices A and B with corresponding eigenvalues λ and μ, then v is also an eigenvector of both A+B and AB. The eigenvalue for A+B is determined to be λ + μ, while the eigenvalue for AB can be derived by multiplying AB by v, utilizing the property that eigenvalues are scalars. The solution emphasizes the importance of linearity and associativity in matrix operations.

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  • Familiarity with matrix addition and multiplication
  • Knowledge of linearity and associativity properties of matrices
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Homework Statement


Suppose that v is an eigenvector of both A and B with corresponding eigenvalues lambda and mui respectively. Show that v is an eigenvector of A+B and of AB and determine the corresponding eigenvalues


Homework Equations





The Attempt at a Solution


Av = lambda*v
Bv = mui*v
this is all i can think of...can someone give me a hint abt the next step?
 
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Add the two equations together, tada! Of course, you'll need to exploit associativity... or linearity... man I am always getting terms confused.
 
Last edited:


u mean like:
(Av +Bv) = lambda*v + mui*v
(A+B)v = (lambda + mui) v
 


Yup! As for finding the eigenvalues of AB, simply multiply AB by v and remember that your eigenvalues are scalars that can move freely.
 
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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