- #1

ElijahRockers

Gold Member

- 270

- 10

## Homework Statement

This question has two parts, and I did the first part already I think.

If B = {u1, u2, ..., un} is a basis for

**V**, and

##v = \sum_{i=1}^n a_i u_i##

and ##w = \sum_{i=1}^n b_i u_i##

Show ##<v,w> = \sum_{i=1}^n a_i b_i^* = b^{*T}a##

Here's how I did it:

##<v,w> = <\sum_{i=1}^n a_i u_i , w> = \sum_{i=1}^n a_i<u_i , w>##

## = \sum_{i=1}^n a_i b_i^* <u_i , u_i> = \sum_{i=1}^n a_i b_i^*##

Thus proved... however in class he mentioned ##a_i = <v,u_i >## for doing this but I'm not sure how... I've tried to examine it but I can't seem to justify it. And I think I did the proof without that, since <v,aw> = a*<v,w>

Second part of the question, where I'm confused, is, verbatim:

Verify ##V = L^2 [-1,1]##, where B is the set of orthonormal Legendre polynomials,

##p_0 (x) = \frac{1}{\sqrt{2}}##

##p_1 (x) = \sqrt{\frac{3}{2}}x##

##p_2 (x) = \sqrt{\frac{5}{8}}(3x^2 -1)##

and

**v,w**are replaced by ##x-x^2## and ##12+x-3x^2##

## Homework Equations

## The Attempt at a Solution

Not really sure where to start... he mentioned a_i = <v, u_i > in class but I don't really feel comfortable with using that here because I don't understand how that's true. ( I feel like it's really simple, and that's why it's bothering me so much) If somebody could point me in the right direction as to why that expression is true, I could probably finish the question..