Well for example take the least squares formula \theta = (X^T X)^{-1} X y. You derive that by setting a derivative to zero, and solving for \theta. If you don't

Well for example take the least squares formula \theta = (X^T X)^{-1} X y. You derive that by setting a derivative to zero, and solving for \theta. If you don't know what a derivative is, then you're just using an equation that came out of nowhere and that you don't understand.