Excuse me for the noob question: Let's assume x3=1, which means y2=8. What's y? Will it be square root of 8?
It will be square root modulo prime of 8
to be precise, it will be 29896722852569046015560700294576055776214335159245303116488692907525646231534
(29896722852569046015560700294576055776214335159245303116488692907525646231534 * 29896722852569046015560700294576055776214335159245303116488692907525646231534) mod secp256k1.p = 8