My Favorite One-Liners: Part 37

In this series, I’m compiling some of the quips and one-liners that I’ll use with my students to hopefully make my lessons more memorable for them.

Sometimes, I’ll deliberately show something wrong to my students, and their job is to figure out how it went wrong. For example, I might show my students the classic “proof” that 1= 2:

x =y

x^2 = xy

x^2 - y^2 = xy - y^2

(x+y)(x-y) = y(x-y)

x + y = y

y + y = y

2y = y

2 = 1

After coming to the conclusion, as my students are staring at this very unanticipated result, I’ll smile with my best used-car salesman smile and say “Trust me,” just like in the old Joe Isuzu commercials.

Of course, the joke is that my students shouldn’t trust me, and they should figure out exactly what happened.

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