Nerdy jokes with Twilight~

My submission for the group! My secret santa child was and they had asked for Twilight telling a nerdy, silly joke!
I'm pretty terrible at math in general so the math joke I actually got from [link]
And apologies if you can't read my handwriting, it says:
Twilight: "This is hilarious, and also true: if a pizza has a radius 'z' and a depth 'a' that pizza's volume can be defined Pi*z*z*a."
Applejack: "Whatever you say sugarcube"

This was lots of fun to do though and I hope everyone likes it, Happy Holidays!

EDIT:
Hey everyone, I'm sorry I haven't been able to respond to all the comments on this one (especially the ones pertaining to the math formula) but I just wanted to say thanks for enjoying the picture so much and having so much fun with it overall. I'm sorry if it's not perfect, I made it in a day before having to leave on a trip to see my family during the holidays, but I may revisit this and fix the speech bubbles so it reads in a much more appropriate order and makes more sense overall for people.
The formula will most likely remain the same though to preserve not only the joke, but also the fact that I found the joke online from another source. Also, I'm pretty bad at math so I'm happy with it as is for the image.

Thank you again though everyone! I really really appreciate all of the comments and favorites on this one! ^.^

Background was obtained via Google images, all characters/assets are © Hasbro