fix typo found by yh36

src/lec02.tex

@@ -178,7 +178,7 @@ \section{Gram-Schmidt Orthogonalization}
   \vdots \\
   \gs{\vecb}_j &:= \vecb_j - \sum_{i < j} \mu_{i,j} \cdot \gs{\vecb}_i
                & \text{where } \mu_{i,j}
-               &= \inner{\vecb_j,\gs{\vecb}_i}/\inner{\gs{\vecb}_j,\gs{\vecb}_j}.
+               &= \inner{\vecb_j,\gs{\vecb}_i}/\inner{\gs{\vecb}_i,\gs{\vecb}_i}.
 \end{align*}
 We can verify that the vectors~$\gs{\vecb}_{j}$ are mutually
 orthogonal. For example,