Quote from: BlackHatCoiner on Today at 06:20:17 PM

Why don't we call them negatives or positives?

Because in finite fields there is no such thing as a negative or positive.

Quote from: BlackHatCoiner on Today at 06:20:17 PM

Does the computer chooses it randomly?

No. When you turn a private key in to a public key, you get exactly one point on the curve, which has exactly one x coordinate and one y coordinate. However, for every x coordinate, there are two possible y coordinates, so when you compress your public key down to just the x coordinate, you specific which y coordinate is the correct one.

Quote from: BlackHatCoiner on Today at 06:20:17 PM

What is p?

The field size, which for the secp256k1 curve bitcoin uses is 2²⁵⁶ – 2³² - 2⁹ - 2⁸ - 2⁷ - 2⁶ - 2⁴ - 1.