What is the equation used to calculate a linear trendline?

I've been looking for this formula in this website so I've made it Q&A style :) Hope this helps.

Slope;

$$\alpha = {n\sum(xy) - \sum x \sum y \over n\sum x^2 - (\sum x)^2}$$

Offset:

$$\beta = {\sum y - \alpha \sum x \over n}$$

Trendline formula:

$$y = \alpha x + \beta $$

source : https://classroom.synonym.com/calculate-trendline-2709.html