Engaging students: Rational and Irrational Numbers

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 Trenton Hicks. His topic, from Pre-Algebra: rational and irrational numbers.

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The big history associated with irrational numbers involves a Greek philosopher, Hippasus, and his peers, the Pythagorean Theorem, and a square. Hippasus had a square with side lengths of 1 unit, raising the question: what is the distance from corner to corner across the square? The pythagorean theorem tells us that it should be the square root of two. After searching for two numbers to represent the square root of two as a ratio, Hippasus sought out something else: proving that it wasn’t rational. He did so by contradiction, assuming that the square root of two was rational, and that said ratio was in simplest terms. By manipulating the equation, he found that one of the integers in the ratio was even. By further manipulation, he found that the other integer was even as well, reaching a paradox. The ratio couldn’t be in simplest terms if both numbers were even. With this, he had proven that there were no two numbers that could represent the square root of two as a ratio. Thus, the concept of an irrational number was born. It is rumored that once he went to present his findings, his peers disapproved. This new idea contradicted their original beliefs, and was even considered blasphemy. Some rumors even suggest he was murdered for this.

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Given the history above, the students could know what it was like for Hippasus and his peers by designing a humorous hypothetical to get them interested in the history. “Imagine you’re in a fellowship of people just like yourselves. You love pizza. You love the toppings, the taste, the artistry. You and your fellow pizza enthusiasts believe that pizza is the language of the universe, and worship it accordingly. One day, you are tasked with cracking a new subcategory of pizza: vegetable pizza. You test vegetables far and wide, and nothing seems to be just what you’re looking for. One day, you see a pineapple sitting on the counter, and you resort to trying it on pizza, since you’re out of ideas. You try it, and it works perfectly. You rush to tell the other pizza enthusiasts and you are shunned for pizza blasphemy. They get so furious with you, that they take you on a boat, and throw you overboard. Your story is very similar to another man’s story, but this man was thrown off a boat for discovering a new set of numbers, not a new flavor of pizza.” Then, to wrap up, the instructor could hand out rulers and squares and tell students to calculate and measure the square’s diagonal corners, to simulate the problem that Hippasus was confronted with.

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By this point, the students should have already seen concepts related to fractions,  pythagorean theorem, square roots, and they may have even heard of pi or the square root of 2. This concept introduces new terminology to describe fractions as “ratios” or “rational” and introduces a new concept of irrational numbers. The most common example, referenced above, uses a square to construct a 45-45-90 triangle, which is also potentially something they have seen before. Ratios in general are a topic directly related to similar triangles. Lastly, in order to compute areas of circles and related geometries, students have had to use the irrational number pi. When first introduced to this number, students may have been told that this number is irrational without any context of what that means. This lesson and curriculum would be a perfect opportunity to fill in those gaps, while addressing any misconceptions about what irrational numbers are. For instance, many students believe that ⅓ is irrational because it cannot be expressed as a finite decimal.

Source: https://nrich.maths.org/2671

Source: https://youtu.be/sbGjr_awePE

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