More Lessons: http://www.MathAndScience.com Twitter: https://twitter.com/JasonGibsonMath In this lesson, you will learn what the mathematical definition of a derivative is in calculus. The derivative is defined to be the slope of the line tangent to a function at a point. In order to do this, we find the slope of a line passing through two far away points, then slowing move these points closer together using the limit process. The derivative is then defined to be the slope of the line tangent to the function at a given point, and is calculated to be the slope of the line through two points, as the limit takes these two points to be infinitely close together.