# problem with \left| and align [duplicate]

Possible Duplicate:
How to make \left, \right pairs of delimiter work over multiple lines?

Hi I'm trying to write a long equation with {align*}:

\begin{align*}
&\left|<L(w^2u),Lu>_k-<L(wu),L(wu)>_k \right|= \\
&|<L(w^2u),Lu>_k-<wL(wu),Lu>_k+<wL(wu),Lu>_k\\
&-<L(wu),wLu>_k+<L(wu),wLu>_k-<L(wu),L(wu)>_k|\\
&\leq \left|<(Lw-wL)(wu),Lu>_k\right|+\left|<wL(wu),Lu>_k-<L(wu),L(wu)>_k\right|\\
&+\left|<L(wu),(wL-Lw)u>_k\right|
\end{align*}


and I find that when I try to add \left| and \right to the second and third line the code doesn't compile. Can someone tell me what is wrong with this and how to fix it:

\begin{align*}
&\left|<L(w^2u),Lu>_k-<L(wu),L(wu)>_k \right|= \\
&\left|<L(w^2u),Lu>_k-<wL(wu),Lu>_k+<wL(wu),Lu>_k\\
&-<L(wu),wLu>_k+<L(wu),wLu>_k-<L(wu),L(wu)>_k\right|\\
&\leq \left|<(Lw-wL)(wu),Lu>_k\right|+\left|<wL(wu),Lu>_k-<L(wu),L(wu)>_k\right|\\
&+\left|<L(wu),(wL-Lw)u>_k\right|
\end{align*}

• A comment not related to pairing \left and \right directives, but about how to write the "angle" symbols around inner products. You shouldn't use < and >, in part because the spacing will be quite wrong. It's much better to use \langle and \rangle. – Mico Sep 12 '12 at 20:48

\left can not live without \right at the same line. You may skip it by adding \right. or \left. which "closes" the line.
\begin{align*}