# Homework Help: Matrix / basis problem

1. Aug 23, 2011

### Lindsayyyy

Hi everyone

1. The problem statement, all variables and given/known data

File at attachment. Given are two basis and the orthogonal matrix B. When r=...(see attachment) I shall proof that the lambdas are equal.

2. Relevant equations

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3. The attempt at a solution

I have much trouble with this exercise and it is quite urgent. I tried to express v1' via v1 and v2, but this doesn't bring me to the solution, for example I have: v1' = av1 + bv2 etc.

Can anyone help me with this?

Thanks for the help in advance

#### Attached Files:

• ###### MATHS.JPG
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2. Aug 27, 2011

### I like Serena

Hi Lindsayyyy!

I don't really get your problem statement.

Any vector r can be represented uniquely with respect to a basis.
With respect to a different basis the representation is again unique, but will always be different.
So as I understand your problem, you can only proof that the lambdas are different.

The lambdas will only be the same iff the 2 basis are the same (that is, if M is the identity matrix).

So I suspect you're not supposed to proof the lambdas are the same.
Especially seeing the last equation saying something about what appears to be the vector norm of an inner product of the lambdas.
Still not quite sure what it says though. Can you clarify?

I can say that vector norm and inner product are preserved by an orthogonal matrix, so you probably need to do something with that.

Last edited: Aug 27, 2011