# Thread: orthogonal polynomials and the recurrence relation

1. ## orthogonal polynomials and the recurrence relation

Let $\displaystyle \langle\cdot,\cdot\rangle$ be an inner product on the real vector space of polynomials, and consider the set $\displaystyle \{p_0,\cdots,p_n,\cdots\}$ of monic orthogonal polynomials defined recursively by

$\displaystyle p_0(x)=1$

$\displaystyle p_1(x)=x-a_1$ and

$\displaystyle p_n(x)=(x-a_n)p_{n-1}-b_np_{n-2}(x)$ for $\displaystyle n\geq 2$,

where $\displaystyle a_n=\frac{\langle xp_{n-1},p_{n-1}\rangle}{\langle p_{n-1},p_{n-1}\rangle}$, and

$\displaystyle b_n=\frac{\langle xp_{n-1},p_{n-2}\rangle}{\langle p_{n-2},p_{n-2}\rangle}$.

Show that $\displaystyle \langle xp_{n-1},p_{n-2}\rangle=\langle p_{n-1},xp_{n-2}\rangle$.
I've been wrestling with this for several days, but I can't crack it. I don't think it's supposed to be difficult though. I suspect I'm just missing something obvious.

Any help would be much appreciated!

2. ## Re: orthogonal polynomials and the recurrence relation

Just a guess but it could be a special polynomial such as Legendre, Chebshev, etc. Look into those, because I don't remember what they look like.