Least Square Estimators - Unbiased Proof

The Simple Linear Regression Least Squared Estimators, b0 and b1, are unbiased. In this video I show the proof. What does it mean for X to not be random? I discuss this more in this video: https://youtu.be/5Ezg9UXIyZs Near minute 4, I mention that Sum(xi - xbar) = 0, here is a video showing this: https://youtu.be/oyjkFmNMMKA Near minute 8, I mention that Sum (xi - xbar)xi = Sum (xi - xbar) * (xi - xbar) = Sxx, here is a video showing this: https://youtu.be/b0FCezzWqIg