### Archive

Archive for December, 2012

## Desmos and LaTex Mashup

Over the past year, I have  created a lot of graphs in Desmos.  A collection of these can found here.  There you will find a wide range of graphs; some  are art related and some are only using sliders.  Also, some of the graphs are lab based and explorations.  These graphs have instructions for students to follow and some blank spots for their answers.  However, I have wanted students to work on paper, too, while working in Desmos.  So, I am now creating a Desmos Lab packet.  This lab packet will look very similar to the Desmos graph, allowing students to work through Desmos and record their work on paper.  Here are the steps if you would also like to create a worksheet/lab for students to follow.

1. Go to this website. http://jsfiddle.net/uRkkM/3/ The directions are in the lower right hand corner.  All you have to do is drag “Equations List” to your bookmarks bar.  Then, “From a Desmos Graph, it will open a new window containing text and latex for the expressions from the expressions list.”
2. Now create a lab or some type of exploration in Desmos.  When done click the “Equations List” and you will see all of the inputs from you Desmos graph that can be copied in LaTex.
3. Finally, polish up your LaTex file.  Now your students have a piece of paper that they can easily follow along with the Desmos graph.

There you go simple as that!  I am excited to try this out with my students.  Here is a link to what my looks like so far. Check it out and let me know if you have any ideas.

Here are is an example of those steps.

• The Desmos graph is here: https://www.desmos.com/calculator/yw9lovl86i
• The input after pressing Equations list looks like this.  I copy it and paste it into a LaTex document
Semi Circle with radius 'a'.
$f\left(x\right)=\sqrt{a^2-x^2}$
$a=4$
Below are two points on the semi-circle, such that the line connecting the two is parallel to the x-axis and is a factor 'b' of the diameter.
$\left(ba,\space f\left(ba\right)\right),\space\left(-ba,\space f\left(-ab\right)\right)$
A factor "b" of the diameter. For example, b=0.5 means that the top blue line half of the diameter. b=0.2 would be two tenths of the diameter, or in other words, one-fifth.
$b=0.8$
Begin by letting a=2 and b=0.5.  What is the height between the two blue lines?
Next let a=4 and b=0.5. What is the height between the two blue lines?
Try more 'a' and 'b' values till you see a pattern.  See if you can write the height as function of b.
Your answer above probably has some trig functions involved.  See if you can write the equivalent algebraic expression.

$H_{eight}\left(x\right)=ax\tan\left(\arccos\left(x\right)\right)$
The equivalent algebraic expression
$y=a\sqrt{1-x^2}$
$\left(b,\space H_{eight}\left(b\right)\right)$
Graphs of the two blue lines.
$y=\left\{-ab\le x\le ab:f\left(ab\right)\right\}$
$y=\left\{-a\le x\le a:0\right\}$
Categories: blah-blah, desmos Tags: , ,

## What can I do for AMATYC?

Below is a reflection on my recent attendance of the 2012 AMATYC Conference, which I submitted to the NCMATYC fall newsletter.

When someone asks me, “Did you have a good conference?”, I often reply, “How could I not?”, and then continue to share all the wonderful events at the conference.  To quickly sum up my AMATYC 2012 experience I got my math on, gave an Ignite talk (https://sites.google.com/site/2point718271827459045/) , got my math on some more, celebrated in the evenings, got my math on, and did my delegate duties.  Feel free to look up my tweets from the conference for some extra inside scoop, #AMATYC12.  Filling in all of the details would take too long, so I will only offer one short experience.

I attended three days straight of amazing session! In each one of those sessions, people would ask thoughtful follow up questions and offer excellent feedback.  For example, I was in a talk that gave some ideas to spice up a trig course.  The person that I was sitting next to mentioned to the presenter, “Just skip the ambiguous case stuff.  Use the Law of Cosines for Angle Side Side and then apply the quadratic formula.”  The presenter paused for a moment and replied exactly with what I was thinking, “I have never thought about it like that.”  That 15 second comment was the golden nugget that I carried away from that session, inspiring me to create this graph of Angle Side Side, which can be seen here https://www.desmos.com/calculator/xubckxlnba, and write a blog entry about it http://t.co/aNGEHAoH.

What happened in that session was not an isolated event, and, as with every other conference I have attended, I have been overwhelmed with great ideas.  Yet, trying to fit in all of those ideas into my currently overwhelmed scheduled just makes me feel more overwhelmed.  Plus, my frugal instinct tells me not to let go of anything because I might find a time to use it. Yeah, right!  That strategy has resulted in stacks of materials gathering dust on my shelf.  Maybe there needs to be a session called “What to do with all that professional development you just had.”  Am I the only one who walks away from an outstanding conference and only applies a small portion of it?

Perhaps there is a difference between an educator who attends conference and one who efficiently applies the conference.  This reminds me of another AMATYC session I attended where the speaker had their students discuss the characteristics between an A student and a C student.  The data in their survey showed that one perception of students is that doing homework is the main characteristic of an A student.  As an educator, I know that being an A student is much more than just attending class and practicing a few exercises.  But let’s make a switch and apply it towards professional development, like an AMATYC conference.   What are the different characteristics of an A teacher versus a C teacher?  Does a C teacher do professional development differently than an A teacher?

My first intention was not to give a talk at AMATYC or to be a NC delegate.   After fulfilling those duties, I am thankful that I had a nudge from our current NCMATYC president to participate in those events.  Being active at the conference helped challenge me professionally.  Plus, just being around other people who are active in AMATYC is inspiring!  Chat with them for a bit and you can see that they have many characteristics of an A teacher.   I hope to carry this motivation forward with AMATYC and NCMATYC.  Not only do I want to attend, I want to be involved.  Not only do I want to participate at the conference, I want contribute throughout the year.  Before going to Jacksonville, my perspective on joining AMATYC was “What could they do for me?”.  I now wonder if this is a characteristic of a C teacher.  I imagine that an A teacher would step up to the challenge and say, “What can I do for AMATYC?”

Categories: blah-blah, presentations Tags: ,

## Standard Deviation of Sunset and Sunrise

Thanks to Kate Owens (@katemath) for sharing a great graph and saying the phrase “standard deviation” in a tweet. I was going to teach standard deviation to my Survey of Math class the next day, so this was perfect timing. The following is how I used the graph in class. Note that in description of the graph, the standard deviation is given.  This was not shown to the students until later. http://visual.ly/daylight-saving-time-explained

• How can you use the graph to figure out what day of the year has the longest night? shortest night?
• Where are the time changes? Does it really save daylight?
• What type of average (mean, median, mode, midrange) do you think is used in the graph?
• How can you use the graph to figure out which has a higher standard deviation, sunset or sunrise?
• Estimate the average sunrise time. What percent of the days have a sunrise earlier than than the average? later than the average.
• (I had two students pick two sun rises times. They were 5:20 and 6:40.)  How many sunsets occur during this time?
• Who would find the above sunrise interval useful? (One idea would be construction workers or people who work outside.)
• This graph is for Chicago, IL. Would it be similar for where we live, Hickory, NC?
• As you moved closer to the equator, would the standard deviation change? What about for a location in Alaska. How would their standard deviation for sunrises be?

I guided the class through those questions in a 50 minute class period.  I liked the activity because the data was in the form of a graph.  Usually, the exercises list out the data and have students calculate every thing. I plan on using the graph again and making a lab exercise about it.

This one caught my eye because I will be teaching summations soon. So, I thought I would look at the sum of the perfect squares. In WolframAlpha can you type sum. I started using upper sums that were powers of 10 and then counting the number of digits in the sum. Do this enough times and you will notice that when the upper sum is $10^a$ the number of digits in the sum will be $3a$. Why does this happen?
First, the number of digits in a number can be found by taking the base ten log of the number and then the ceiling. For example, $5^{500}$ would have $ceil(500 \log_{10} (5))$ number of digits. Knowing this we can find out how many digits there are in sum of squares. Using the sum of squares formula $(1/6)n(n+1)(2n+1)$, take $ceil(\log_{10} (1/6)n(n+1)(2n+1)$ and now we can quickly find the number of digits in a sum. Note that for students this would be a good time to recap log properties.
Second, I went to desmos.com and created a slider for different $n$ values. I defined $n$ to be $n=b^a$ Here are a few $n$ values that create 140 digit numbers. $2^{155}, 3^{98}, 6^{60}, 9^{49}, 13^{42}$ Some neat patterns begin to show. $46^{23}, 47^{23}$ are the first pair of consecutives with the same exponent. $87^{24}, 88^{24}, 89^{24}$ are the first trio. My favorite so far is $62^{26}$ I stopped searching for $b=110$ and started search for $a=2$, that is some number $b$ squared that would make a 140 digit number. I found that $(2*10^{23})^2$ is one. Wow, this means that b value goes from 2 to at least $2*10^{23}$ One could create a program and find just how many $n=b^a$ values there are. I only found 25 of them. Also, what would be the largest amount of consecutive b values – that is $b^{a}, (b+1)^a, (b+2)^a, (b+3)^n...$