Inner product generated by matrix

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The discussion focuses on calculating the inner product defined by a specific matrix for vectors u = (-1, 2) and v = (2, 5). The initial attempt at finding the inner product resulted in an incorrect equation, leading to a discrepancy in the distance calculation d(u, v). The correct inner product should include cross terms u1v2 and u2v1, which were overlooked. The participant's final calculation yielded a different result than the textbook answer, prompting a request for verification of the inner product calculation. The resolution emphasizes the importance of including all relevant terms in matrix-based inner product calculations.
derryck1234
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Homework Statement



Find d(u, v), where the inner product is defined by the matrix

[1 2]
[-1 3]

and u = (-1, 2), v = (2, 5)

Homework Equations



<u, v> = Au . Av
d(u, v) = abs(u - v)

The Attempt at a Solution



I first tried to find the resulting inner product from the matrix in terms of an equation:

I got it to be:

2u1v1 + 13u2v2

Then I simply found u - v, which came to be (-3, -3)

And thus d(u, v) = <-3, -3>0.5

This, in terms of the relevant inner product, is:

[2(9) + 13(9)]0.5

Unfortunately, the books answer does not agree? It says it is 3 times root 13. I get root 135?
 
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Check your inner product calculation. There should be some u1v2 and u2v1 terms
 
Thanks.
 
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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