MATH 215/255
Fall 2014
Comments about Homework 7
1) 6.4.1: Done perfectly by most students. Only mistakes were either sign errors or
omitting the shift when taking the inverse Laplace transforms. Another mistake made
by a couple of students was leaving out the X(s) term when taking the Laplace
transform (i.e. writing X(s)(s2 + s) = 1).
2) 3.1.2: Multiple students attempted to get a second order O.D.E. for x1 , but lost marks
due to many algebraic mistakes. Those solving with the system method (eigenvalues,
eigenvectors) did not take into account the particular solution. General solution means
homogeneous solution.
3) 3.1.102: Done well by most students. Some used method in solutions, other did the
standard procedure with matrices.
4) 3.3.2: Done well for the most part, with students primarily losing marks for incompleteness.
5) 3.3.104: Not done well by the majority of students. A lot of them treated it as a
constant coefficients problem.