# Friend passed me this note after lecture

After my linear algebra lecture ended at 3:30 today, my friend passed me this note, but it seems to be encrypted in some way that I don't understand. What question is my friend asking, and what is the answer?

Feedback is appreciated, and I will add hints if necessary.

Hint 1:

There is a very good reason the characters look the way they do. It's not a simple substitution cipher.

Hint 2:

What does The class I'm Taking have To do with The cipher?

• Does linear algebra have anything to do with the answer? Commented Mar 25, 2018 at 17:48
• @GrantGarrison That is a good question. Commented Mar 25, 2018 at 17:54
• im sure another good question would be about the significance of ending at 3:30
– tom
Commented Mar 26, 2018 at 1:06
• @tom I forget, was it 3:30 or 6:15? I always get the hour and minute hands mixed up :) Commented Mar 26, 2018 at 1:19
• All of the Ts in the second hint are capitolized. I am thinking we need to transpose the message. Commented Mar 26, 2018 at 21:25

First of all, great puzzle! I am currently in Linear Algebra myself.

As is hinted with the capitalization of 'T' in hint 2, we first take the transpose of the whole message

Then rewrite the message with the rows side by side.

This gives the outlines of block letters, which reads as: WHAT MATRIX OPERATION DID WE LEARN TODAY?

The answer to this is, of course, matrix transposition.

• Hey, you got it! Just so you know, there was also a subtle hint in 3:30 vs 6:15 in the comments. In those times, the hour hand and minute hand swap horizontal/vertical positions. Commented Mar 26, 2018 at 23:26
• @tyobrien - I've edited your answer to make it clearer what Riley's friend was asking, since it took me a few attempts to see it. Commented Mar 27, 2018 at 3:05
• This is super clever! Commented Mar 27, 2018 at 16:39
• Man, I cant even understand it reading this answer. LOL Commented Apr 7, 2018 at 4:41

• Hmm, you might be onto something. :) But keep Hint 1 in mind. And one hint: The transpose of $\begin{bmatrix}8&8\\8&8\end{bmatrix}$ is not $\begin{bmatrix}\infty&\infty\\\infty&\infty\end{bmatrix}$ Commented Mar 26, 2018 at 22:09