Engaging students: The field axioms

In my capstone class for future secondary math teachers, I ask my students to come up with ideas for engaging their students with different topics in the secondary mathematics curriculum. In other words, the point of the assignment was not to devise a full-blown lesson plan on this topic. Instead, I asked my students to think about three different ways of getting their students interested in the topic in the first place.

I plan to share some of the best of these ideas on this blog (after asking my students’ permission, of course).

This student submission again comes from my former student Andrew Sansom. His topic, from Pre-Algebra: the field axioms of arithmetic (the distributive law, the commutativity and associativity of addition and multiplication, etc.).

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Algebra, from one perspective, is the use of numbers’ and operations’ properties to manipulate expressions. Some of these properties, called the field axioms, are crucial to being able to easily solve equations. These properties include associativity, commutativity, distributivity, identity, and inverse. To better appreciate how these properties are so helpful in algebra, it is useful to explore some examples of operations that do not obey these laws.

A1. What interesting (i.e., uncontrived) word problems using this topic can your students do now?

Example 1: The Average (Mean) is Not Associative

Part 1
A math teacher Mrs. Taylor instructs a class of three students: Alice, Bob, and Charlie. The class took an exam last week, but Charlie was sick and missed the test, so he took it today. Mrs. Taylor promised the class that if the class average on the exam was high enough, she would give them all candy. If Alice scored a 96 and Bob scored an 83, what was the class average (the average of those two students) after the first day of the exam?

mean(A,B)= \frac{(A+B}{2}=

Part 2
After Charlie took the exam (he scored an 89), Mrs. Taylor wanted to know if she had to calculate the average from scratch (i.e. add all three scores and divide by three), or if she could just average the previous mean and Charlie’s score (i.e. add your answer from part 1 and Charlie’s score and divide by 2), since she already had done some arithmetic and didn’t want to waste time. Would she find the same answer if she tried both methods? If not, which one is correct? Why?
mean(mean(A,B),C)= \frac{ \frac{A+B}{2} +C}{2} =

mean(A,B)= \frac{A+B+C}{3}=

Part 3
After her discovery in Part 2, Mrs. Taylor is curious if she first found the mean of Bob and Charlie’s grades, then averaged it with Alice’s grade, if it would be the same as an answer above. Is it? Why or why not?

mean(A,mean(B,C))=\frac{A+ \frac{B+C}{2} }{2}=

Part 4
What does it mean for an operation to be associative? How does this activity show that the average (mean) is not associative? Why does this mean you have to be extra careful when solving problems with averages?

Example 2: Subtraction is Not Commutative

Part 1
Mrs. Taylor likes to visit Alaska during the summer. When she arrived in Anchorage, it was 10F, but a snowstorm caused the temperature to drop by 21F. Write an equation with subtraction to find the new temperature the next day.

The next summer, when Mrs. Taylor arrives in Anchorage, it is 21F but the temperature drops 10F. Write an equation with subtraction to find the new temperature the next day.

Part 2
What does it mean for an operation to be commutative? Based on what you found in Part 1, is subtraction commutative? Why or why not? Why does that mean you need to be extra careful when solving problems with subtraction?

 

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B2. How does this topic extend what your students should have learned in previous courses?

Prior to pre-algebra, students should be proficient in arithmetic. In that study, they should have been exposed to fact families, which are simple examples of the inverse elements of addition and multiplication. The field axioms generalize these ideas to other objects. Students also should have realized that subtraction and division do not commute, though they likely never used that name. They also likely realized that addition by 0 or multiplication by 1 do not affect the value of the other element. By learning the names of these different properties, students build upon their prior experience to be able to label and acknowledge when these properties appear in other contexts.

 

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B1. How can this topic be used in your students’ future courses in mathematics or science?

Although high school students will spend most of their time working in fields, instead of other algebraic structures such as non-Abelian groups or noncommutative rings, an appreciation and awareness of the field axioms while studying pre-algebra will prepare them for solving equations involving exponents (for example, intuitively questioning whether 2^x=x^2, which are trivially different, but not obvious to the novice). Furthermore, most Algebra II classes do briefly study Matrix Algebra, which is noncommutative (i.e. matrix multiplication does not commute), which causes many interesting conundrums for the uninitiated student while trying to solve problems. This appreciation of the field axioms prepares them for later study in Linear Algebra and Abstract Algebra. Outside of their math classes, vector fields form a critical part of physics, even at the high school level. Although most high school students do not realize it, they have to use the field axioms all the time to solve physics problems.

References:
Use of the mean as a simple example of a non-associative operation courtesy of StackExchange user “Accumulation” on the thread “Non-Associative Operations” (https://math.stackexchange.com/a/2892589)

 

Predicate Logic and Popular Culture (Part 206): Jack Johnson

Let H be the set of all things, let T be the set of all times, let G(x) be the proposition “x is good,” and let R(x,t) be the proposition “x remains at time t.” Translate the logical statement

\forall x \in H(G(x) Longrightarrow \forall t \in T(R(x,t))).

This matches a line from “Mudfootball” by Jack Johnson.

Context: Part of the discrete mathematics course includes an introduction to predicate and propositional logic for our math majors. As you can probably guess from their names, students tend to think these concepts are dry and uninteresting even though they’re very important for their development as math majors.

In an effort to making these topics more appealing, I spent a few days mining the depths of popular culture in a (likely futile) attempt to make these ideas more interesting to my students. In this series, I’d like to share what I found. Naturally, the sources that I found have varying levels of complexity, which is appropriate for students who are first learning prepositional and predicate logic.

When I actually presented these in class, I either presented the logical statement and had my class guess the statement in actual English, or I gave my students the famous quote and them translate it into predicate logic. However, for the purposes of this series, I’ll just present the statement in predicate logic first.

Predicate Logic and Popular Culture (Part 205): Bob Marley

Let T be the set of all things, let L(x) be the proposition “x is a little thing,” and let A(x) be the proposition “x is going to be all right.” Translate the logical statement

\forall x \in T(L(x) \Longrightarrow A(x)).

This matches a line from “Three Little Birds” by Bob Marley.

Context: Part of the discrete mathematics course includes an introduction to predicate and propositional logic for our math majors. As you can probably guess from their names, students tend to think these concepts are dry and uninteresting even though they’re very important for their development as math majors.

In an effort to making these topics more appealing, I spent a few days mining the depths of popular culture in a (likely futile) attempt to make these ideas more interesting to my students. In this series, I’d like to share what I found. Naturally, the sources that I found have varying levels of complexity, which is appropriate for students who are first learning prepositional and predicate logic.

When I actually presented these in class, I either presented the logical statement and had my class guess the statement in actual English, or I gave my students the famous quote and them translate it into predicate logic. However, for the purposes of this series, I’ll just present the statement in predicate logic first.

Predicate Logic and Popular Culture (Part 204): Billy Joel

Let T be the set of all times, and let W(t) be the proposition “She is a woman to me at time t.” Translate the logical statement

\forall t \in T( W(t)).

This matches a line from “She’s Always a Woman” by Billy Joel.

Context: Part of the discrete mathematics course includes an introduction to predicate and propositional logic for our math majors. As you can probably guess from their names, students tend to think these concepts are dry and uninteresting even though they’re very important for their development as math majors.

In an effort to making these topics more appealing, I spent a few days mining the depths of popular culture in a (likely futile) attempt to make these ideas more interesting to my students. In this series, I’d like to share what I found. Naturally, the sources that I found have varying levels of complexity, which is appropriate for students who are first learning prepositional and predicate logic.

When I actually presented these in class, I either presented the logical statement and had my class guess the statement in actual English, or I gave my students the famous quote and them translate it into predicate logic. However, for the purposes of this series, I’ll just present the statement in predicate logic first.

Predicate Logic and Popular Culture (Part 203): Bill Withers

Let P be the set of all people, let T be the set of all times, let P(x,t) be the proposition “x has pain at time t,” and let S(x,t) be the proposition “x has sorrow at time t.” Translate the logical statement

\forall x \in P( \exists t_1 \in T(P(x,t)) \land \exists t_2 \in T(S(x,t)).

This matches a line from “Lean on Me.” Note: while I think the translation above matches the intent of the song, a case could be made that, literally rendered, the “there exists” symbols should come first — that there’s a single time that everyone has pain at that one time.

Context: Part of the discrete mathematics course includes an introduction to predicate and propositional logic for our math majors. As you can probably guess from their names, students tend to think these concepts are dry and uninteresting even though they’re very important for their development as math majors.

In an effort to making these topics more appealing, I spent a few days mining the depths of popular culture in a (likely futile) attempt to make these ideas more interesting to my students. In this series, I’d like to share what I found. Naturally, the sources that I found have varying levels of complexity, which is appropriate for students who are first learning prepositional and predicate logic.

When I actually presented these in class, I either presented the logical statement and had my class guess the statement in actual English, or I gave my students the famous quote and them translate it into predicate logic. However, for the purposes of this series, I’ll just present the statement in predicate logic first.

Predicate Logic and Popular Culture (Part 202): The LEGO Movie

Let T be the set of all things, let p be the proposition “You’re part of a team,” let A(x) be the proposition “x is awesome,” and let C(x) be the proposition “x is cool.” Translate the logical statement

p \Longrightarrow \forall x in T(A(x) \land C(x)).

This matches the opening line of “Everything is Awesome!!!” from The LEGO Movie.

Context: Part of the discrete mathematics course includes an introduction to predicate and propositional logic for our math majors. As you can probably guess from their names, students tend to think these concepts are dry and uninteresting even though they’re very important for their development as math majors.

In an effort to making these topics more appealing, I spent a few days mining the depths of popular culture in a (likely futile) attempt to make these ideas more interesting to my students. In this series, I’d like to share what I found. Naturally, the sources that I found have varying levels of complexity, which is appropriate for students who are first learning prepositional and predicate logic.

When I actually presented these in class, I either presented the logical statement and had my class guess the statement in actual English, or I gave my students the famous quote and them translate it into predicate logic. However, for the purposes of this series, I’ll just present the statement in predicate logic first.

Predicate Logic and Popular Culture (Part 201): Hamilton

Let T be the set of all times, let time 0 be now, and let L(t) be the proposition “I like the quiet at time t.” Translate the logical statement

\forall t \in T(t < 0 \longrightarrow \lnot L(t)).

This matches a line from “It’s Quiet Uptown” from the hit musical Hamilton.

Context: Part of the discrete mathematics course includes an introduction to predicate and propositional logic for our math majors. As you can probably guess from their names, students tend to think these concepts are dry and uninteresting even though they’re very important for their development as math majors.

In an effort to making these topics more appealing, I spent a few days mining the depths of popular culture in a (likely futile) attempt to make these ideas more interesting to my students. In this series, I’d like to share what I found. Naturally, the sources that I found have varying levels of complexity, which is appropriate for students who are first learning prepositional and predicate logic.

When I actually presented these in class, I either presented the logical statement and had my class guess the statement in actual English, or I gave my students the famous quote and them translate it into predicate logic. However, for the purposes of this series, I’ll just present the statement in predicate logic first.

Predicate Logic and Popular Culture (Part 200): Spider-Man

Let T be the set of all times, and let R(t) be the proposition “I will rest at time t,” and let M(t) be the proposition “You are unmasked and eliminated at time t.” Translate the logical statement

\forall t \in T(\lnot M(t) \Longrightarrow \lnot R(t)).

This matches a line by J. Jonas Jameson in the 1990s Spider-Man cartoons.

Context: Part of the discrete mathematics course includes an introduction to predicate and propositional logic for our math majors. As you can probably guess from their names, students tend to think these concepts are dry and uninteresting even though they’re very important for their development as math majors.

In an effort to making these topics more appealing, I spent a few days mining the depths of popular culture in a (likely futile) attempt to make these ideas more interesting to my students. In this series, I’d like to share what I found. Naturally, the sources that I found have varying levels of complexity, which is appropriate for students who are first learning prepositional and predicate logic.

When I actually presented these in class, I either presented the logical statement and had my class guess the statement in actual English, or I gave my students the famous quote and them translate it into predicate logic. However, for the purposes of this series, I’ll just present the statement in predicate logic first.

Predicate Logic and Popular Culture (Part 199): Justin Bieber

Let T be the set of all times, let K(t) be the proposition “You knock me down at time t,” and let G(t) be the proposition “I am on the ground at time t.” Translate the logical statement

\forall t \in T(K(t) \longrightarrow \lnot (\forall s \ge t (G(s)))).

This matches part of the chorus of “Never Say Never” by Justin Bieber.

Context: Part of the discrete mathematics course includes an introduction to predicate and propositional logic for our math majors. As you can probably guess from their names, students tend to think these concepts are dry and uninteresting even though they’re very important for their development as math majors.

In an effort to making these topics more appealing, I spent a few days mining the depths of popular culture in a (likely futile) attempt to make these ideas more interesting to my students. In this series, I’d like to share what I found. Naturally, the sources that I found have varying levels of complexity, which is appropriate for students who are first learning prepositional and predicate logic.

When I actually presented these in class, I either presented the logical statement and had my class guess the statement in actual English, or I gave my students the famous quote and them translate it into predicate logic. However, for the purposes of this series, I’ll just present the statement in predicate logic first.

Predicate Logic and Popular Culture (Part 198): Smash Mouth

Let P be the set of all people, let T be the set of all times, and let R(x,t) be the proposition “x told me at time t that the world is going to roll me. Translate the logical statement

\exists x \in P \exists t \in T (R(x,t)).

This matches the opening line of “All Star” by Smash Mouth.

Context: Part of the discrete mathematics course includes an introduction to predicate and propositional logic for our math majors. As you can probably guess from their names, students tend to think these concepts are dry and uninteresting even though they’re very important for their development as math majors.

In an effort to making these topics more appealing, I spent a few days mining the depths of popular culture in a (likely futile) attempt to make these ideas more interesting to my students. In this series, I’d like to share what I found. Naturally, the sources that I found have varying levels of complexity, which is appropriate for students who are first learning prepositional and predicate logic.

When I actually presented these in class, I either presented the logical statement and had my class guess the statement in actual English, or I gave my students the famous quote and them translate it into predicate logic. However, for the purposes of this series, I’ll just present the statement in predicate logic first.