# Monthly Archives: February 2014

## Where’s Prof. Reitz? And other details

Hi everyone,

I just wanted to provide a quick update.

1.  I was out sick today (Tuesday, 2/25) – stomach flu.  This is not recommended.  Hope you all had a better day than I did.  Luckily, I feel much better now.

2.  I will be out of town for 1 week starting tomorrow, so you will have a sub for the next two classes.

3. There will be no office hours on Thursday 2/27.

4. A reminder – your first exam will take place on Tuesday, 3/4 (next week).

5.  There is NO WeBWorK due next week (3/4), but there will be WeBWorK due the following week based on Exact Equations and Euler’s Method.

Finally, I will be checking email while I am away, but not as often as usual – feel free to write if you have questions or problems.

Regards,
-Prof. Reitz

## Exam #1 Review Sheet UPDATES

Hi everyone,

I’ll post updates & corrections to the review sheet here – check back often for the latest.

• UPDATE #1:  Corrected answer to problem 1 (exponent should have -1/30t, instead of 1/30t)
• UPDATE #2: Corrected answer to problem 4 (exponent in the denominator should be 14, not 13)
• UPDATE #3: Corrected answer to problem 8 (things were off – something was clearly wrong with the left hand side)

## No class this Thursday

This Thursday, 2/20/14, runs on a Monday Schedule – we will not have class, and I will not have office hours.

-Prof. Reitz

## Exam #1: Date Change, and Review Sheet

The date for the first exam has been changed – it will now take place on Tuesday, March 4th.  A review sheet has been posted here.  If you find an error, please let me know in class, on the OpenLab, or by email.

Best,
Prof. Reitz

## Yes, we do have class today!

Hi everyone,

Despite the horrible weather, the college is officially open today – so we will be holding class.  However, I understand that some of you will not be able to make it.  Please read pp68-71 in the book, do your best to understand.

There will NOT be a new WeBWorK for today – your only assignment due next Tuesday is WeBWorK #3b (from last class).

Jonas

## Office Hours this week

Hi everyone,

My office hours on Thursday will be interrupted:

Office Hours Thurs 3/13: 11:00-11:30, and 12:30-1:00

However, I am going to add an additional hour tomorrow (Tuesday) – this will also give you a chance to see me before WeBWorK is due.

Office Hours Tues 3/11:  1pm-2pm

All office hours take place in N707.

Best regards,
Prof. Reitz

## Integrating Factors: A Shortcut

Shortcuts are dangerous things – they may save you time, but they usually don’t help you understand the problem.  Because of this, it’s usually important to have a thorough grasp of the basic idea of how to solve a problem before learning the shortcut.  Since you’ve had a week or so wrestle with the “Integrating Factors” problem, I wanted to share a standard shortcut (covered in the text, but not yet discussed in class) for solving these problems, which condenses much of the algebra into two formulas.  You are welcome to use it, or not, as you prefer.

### Shortcut for solving Integrating Factors problems:

Step 1:  Rewrite the differential equation in the standard form:

$\frac{dy}{dt} + p(t)y = g(t)$

In practice, this usually just means getting the $y$ and $\frac{dy}{dt}$ on the same side, and dividing to get rid of anything in front of the $\frac{dy}{dt}$.

Step 2:  Find $\mu$, by plugging in:

$\mu = e^{\int p(t) dt}$

That is, integrate the function in front of $y$, and then raise $e$ to the power of the result.  This gives $\mu$

Step 3:  Find $y$, by plugging in:

$y = \frac{1}{\mu(t)} \int \mu(t) g(t) dt + C$

That is, multiply $\mu$ by the function $g(t)$ from the right hand side of the differential equation, integrate, and multiply the result by $\frac{1}{\mu}$.

NOTE: The standard form mentioned in Step 1 shows up a lot – in fact, even if you are not using the shortcut formulas above, it is considered “pretty standard” to rewrite your equation in standard form before solving the problem.

Happy shortcutting,
-Prof Reitz

## OpenLab Assignment 1: General Education

This assignment is due Thursday, February 13, at the start of class.

The Syllabus for the course lists 8 different “Learning Outcomes” (they appear near the bottom of the Course Information page).  These are the things that we’d like you all to get out of the course.  They  are split into two groups – there are four Learning Outcomes that are directly related to Differential Equations, and then four General Education Learning Outcomes that are not specific to Differential Equations but nonetheless are important elements of this course.  In this assignment I’m going to ask you to focus on the Gen Ed Learning Outcomes.

Assignment.   Choose one of the four Gen Ed Learning Outcomes for the class (they are listed below).   Write a comment in reply to this post (click “Leave a Reply” below), responding to EACH of the following. Write 1-2 paragraphs total.  Begin by telling us which topic you chose.

1. Copy the Learning Outcome word-for-word.
2. Explain what you think it means in your own words.
3. Describe a time that you have used this skill in your past.
4. Do you think this skill will be important in your career? Why or why not?

LIST OF GEN ED LEARNING OUTCOMES FOR MAT 2680.

1. Gather, interpret, evaluate, and apply information discerningly from a variety of sources.

2. Understand and employ both quantitative and qualitative analysis to solve problems.

3. Employ scientific reasoning and logical thinking.

4. Communicate effectively.

Extra Credit.  For extra credit, write a response to one of your classmates’ comments.  Do you feel the same, or different?  Did you learn anything?

## Tutoring for MAT 2680

The Math Department provides free tutoring by Math Specialists four days a week. They are (in the words of my colleague) “experts at Differential Equations”.  This is a fantastic resource.  I’ll paste the schedule below – see the attached flyer for more details.

SCHEDULE:
MONDAYS & WEDNESDAYS 1:00PM-6:00PM IN N604
THURSDAYS 3:00PM TO 6:00PM IN N604
FRIDAYS 10:00AM-4:00 PM IN N723

Spring 2014 Math Tutoring flyer

## 1 Week Extension to deadline for WeBWorK Assignment #1-Modeling-IVPs

Hi everyone,

I realize that many of you are struggling to complete the first two WeBWorK assignments by the due date of this evening at midnight.  For a number of reasons, I’m giving a one-time extension on the deadline for Assignment #1 ONLY.  It will now be due next Tuesday, Feb 12, at midnight.

NOTE: Assignment #0 is still due tonight.

• What are the reasons?  It’s the first assignment, so you are grappling with learning WeBWorK, you are sorting out problems with your logins/passwords on the system, and you are trying to remember how to do basic integrations from Calc II.  That’s a lot!  I’d rather you take a little more time, then simply not complete it.
• Will I regret this? Maybe.
• Will I ever do it again? No way!

Best regards,
Prof. Reitz