The prover needs to provide an Opening Triplets (OT) = (z, f(z), Cₕ) to the verifier. z is chosen by verifier, f(z) can be easily computed as prover has the polynomial, but what is Cₕ? We start with f(x) — f(z) f(z) — f(z) = 0, we know x = z must be a root, so there exists h(x) such that f(x) — f(z) = (x-z) * h(x) h(x) = (f(x) — f(z)) / (x-z)