TOPIC: ETC Calculation = bac-ev/cpi how ?

i have purchase the formulas guide currently i am in studying for EVM Forecasting. i got confusion regarding to this formula :
ETC = (BAC-EV) / CPI
its mentioned in this link :https://www.project-management-prepcast.com/kunena/pmp-exam-discussion/2973-etc-formula-atypical-case
by Mr. Cornelius Fichtner
but as i study in the guide i didn't see a reference for this formula
can you please guide me on this please

ETC = BAC- AC

---

CPI= EV/AC
Which is AC = EV/CPI

Replace above in first formula
ETC = BAC-EV/CPI


CLEAR?

thanks a lot i got it clearly

yes clear now