cleaning up typos

doc/src/week38/week38.do.txt

@@ -441,7 +441,7 @@ the sum $\sum_{i=0}^{n-1} X_{ij}$
 can be rewritten as
 !bt
 \[
-\sum_{i=0}^{n-1} \left(X_{ij} - \frac{1}{n}\sum_{i=0}^{n-1} X_{ij}) = \sum_{i=0}^{n-1} X_{ij} - \sum_{i=0}^{n-1} \frac{1}{n} \sum_{i=0}^{n-1}X_{ij},
+\sum_{i=0}^{n-1} \left(X_{ij} - \frac{1}{n}\sum_{i=0}^{n-1} X_{ij}\right) = \sum_{i=0}^{n-1} X_{ij} - \sum_{i=0}^{n-1} \frac{1}{n} \sum_{i=0}^{n-1}X_{ij},
 \]
 !et
 resulting in
@@ -464,7 +464,7 @@ or
 \beta_0 = \frac{1}{n}\sum_{i=0}^{n-1} y_i = \overline{\bm{y}},
 \]
 !et
-the average value of $\bm{y]$.
+the average value of $\bm{y}$.
 
 Replacing $y_i$ with $y_i - \beta_0 = y_i - \overline{\bm{y}}$ in the cost function will give us (in vector-matrix disguise)
 !bt
@@ -506,7 +506,7 @@ y = np.exp(-x**2) + 1.5 * np.exp(-(x-2)**2)
 
 Maxpolydegree = 20
 X = np.zeros((n,Maxpolydegree))
-We include explicitely the intercpt column
+#We include explicitely the intercept column
 X[:,0] = 1.0
 
 for degree in range(Maxpolydegree):