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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?

jjj

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?

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

2 Answers 2

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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
enter image description here

Then rewrite the message with the rows side by side.
enter image description here

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.

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    $\begingroup$ 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. $\endgroup$
    – Riley
    Mar 26, 2018 at 23:26
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    $\begingroup$ @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. $\endgroup$
    – Phylyp
    Mar 27, 2018 at 3:05
  • $\begingroup$ This is super clever! $\endgroup$ Mar 27, 2018 at 16:39
  • $\begingroup$ Man, I cant even understand it reading this answer. LOL $\endgroup$
    – Jun Rikson
    Apr 7, 2018 at 4:41
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Partial Answer:

The references to linear algebra and the capital Ts in the hint suggest that a transpose operation may be in order to read the message. I took the original image and transposed it as you would when taking the transpose of a matrix. The fact the letters are aligned to still make rows makes me think this may be the right track. transposed image

After getting this, with the new message I:

tried placing a unique letter to represent each symbol to use in a substitution cypher: abaz acde aba cdee ywx afag hecd eafa ia j aja abah akh caei a de fjac la ? Unfortunately, I didn't get anywhere with this.

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    $\begingroup$ 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 $\begin{bmatrix}\infty&\infty\\\infty&\infty\end{bmatrix}$ $\endgroup$
    – Riley
    Mar 26, 2018 at 22:09
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    $\begingroup$ Brilliant comment, @Riley :-) $\endgroup$
    – Phylyp
    Mar 27, 2018 at 3:05

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