Update week35.do.txt

doc/src/week35/week35.do.txt

@@ -536,6 +536,11 @@ on the other hand $\bm{y}$ is a scalar, the Jacobian becomes a
 $1\times n$ matrix.
 
 
+When this matrix is a square matrix $m=n$, its determinant is often referred to as the Jacobian
+determinant. Both the matrix and (if $m=n$) the determinant are
+often referred to simply as the Jacobian. The Jacobian matrix represents the differential of $\bm{y}$ at every point where the
+vector is differentiable. 
+
 !split
 ===== Derivatives, example 1 =====
 
@@ -562,6 +567,8 @@ From this we have, using the definition of the Jacobian
 \]
 !et
 
+!split
+===== Example 2 =====