# Exercise H.2.3 Minor Algebra

Hi all,

Would appreciate it if someone could show the explicit steps on how the second underlined term was derived from the first term underlined.

When I was following through with it, I ended up with the last term being
2 \cos(\alpha t) \sin(\alpha t) \langle Y \rangle _0 and not
-2 \cos(\alpha t) \sin(\alpha t) \langle Y \rangle _0

The rest of the work makes sense, it’s just the simplification of this term which I’m confused about. Below are the explicit steps which I’ve followed to simplify the first underlined term.

Thanks!
-Pavan

Hi Pavan! If I am not mistaken, XZ = iY, you have the signs changed. You can check it by multiplying both matrices

Ok but when multiplied together it’s XZ = -iY as I had in the picture. The second last line in the exercise solution also states that ZX = -XZ = iY meaning that XZ = -iY.

I’m now beginning to think this might actually just be a simple typo. Otherwise, let me know if you see a mistake in my steps.

Hi @Pavan , thank you for asking this question!

I don’t see any mistake in your steps. I too think it was a typo. We’re checking with the person who wrote this node and will be back soon with a definitive answer!

1 Like

Sounds good @CatalinaAlbornoz , I read on the codebook that you want typos flagged through GitHub issues and not on the general forum so let me know if you’d like me to submit an issue on GitHub and delete this post.

I would have done that before if I had recognized it, sorry about that.

Hi @Pavan, no problem!

Sometimes it’s hard to tell if it’s a typo . I’ve confirmed with the person who wrote the node and he’ll do the fix so no need to submit an issue this time.