Revealing cards sorcery
Yes, you not only need to show all five cards, you need to show which of those you picked.

No action is taken in secret; all players are to be made aware of all actions taken and what they effect. And since the cards are revealed when you pick them, they get to know not just what card you picked, but it's name as well.


  701.14a To reveal a card, show that card to all players for a brief time. If an effect causes a card to be revealed, it remains revealed for as long as necessary to complete the parts of the effect that card is relevant to. If the cost to cast a spell or activate an ability includes revealing a card, the card remains revealed from the time the spell or ability is announced until the time it leaves the stack.


(Emphasis mine)