Ti-Basic（Ti-84 Plus）那是什么：»Real（12，Str1，Str2）→Str3«以及如何使其工作？

So there is this Calculator my teacher gave me to try to fix a program that worked in a previous version (probably the Ti-83). According to her it should give the derivation of an equation. The input is self-explaining and the rest of the code is rather simple:So there is this Calculator my teacher gave me