Until when ethereum will continue to decline, will it touch at the price of $ 50?

It shouldn't have fallen like this.
December this year is very different from December 2017. The situation is reversing.

Maybe it can happen if their some bad news appears about eth again, but i don't think any bad news will appear in the end of december. Eth price will rise again and will hit more than $100, after christmas i think eth will back to $200.
boring prediction, rather than just continuing to predict, it's better if you start buying it at this cheap price, to be able to make you one of the richest people with high profits