I was learning dollar-weighted return and I was a bit puzzled by the following and I would like to have some advice.

I understand that it's basically the internal rate return, but using simple interest.

So, letting $A=$ initial amount, $C_k=$ amount of cash-flow at time $0<t_1< \cdots <t_k< \cdots <t_n < 1$, $B=$ the balance at the end of the year and $i=$ the internal rate of return, my understanding is that we have a relationship

$$A(1+i)+\Sigma_{k=1}^{n}C_k(1-t_k)i=B$$

To me this makes sense and is easy to remember, but the book focused on the solution, $i$ as in

$$i = \frac{B-[A+\Sigma_{k=1}^{n}C_k]}{A+\Sigma_{k=1}^{n}C_k(1-t_k)}$$

which DOES make sense but I hardly find it useful to memorize. Practically speaking, is this formula so useful that it is definitely worth while memorizing or do you think it's okay to leave it as something that I should be able to derive but not necessarily derive?