# 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? – Grant Garrison Mar 25 '18 at 17:48
• @GrantGarrison That is a good question. – Riley Mar 25 '18 at 17:54
• im sure another good question would be about the significance of ending at 3:30 – tom Mar 26 '18 at 1:06
• @tom I forget, was it 3:30 or 6:15? I always get the hour and minute hands mixed up :) – Riley Mar 26 '18 at 1:19
• All of the Ts in the second hint are capitolized. I am thinking we need to transpose the message. – Barker Mar 26 '18 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. – Riley Mar 26 '18 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. – Phylyp Mar 27 '18 at 3:05
• This is super clever! – Ben Richards Mar 27 '18 at 16:39
• Man, I cant even understand it reading this answer. LOL – Jun Rikson Apr 7 '18 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 $\begin{bmatrix}\infty&\infty\\\infty&\infty\end{bmatrix}$ – Riley Mar 26 '18 at 22:09