### Overview

This session provides a brief overview of Unit 1 and describes the derivative as the slope of a tangent line. It concludes by stating the main formula defining the derivative.

### Lecture Videos and Notes

#### Video Excerpts

- Clip 1: Introduction to 18.01
- Clip 2: Geometric Interpretation of Differentiation
- Clip 3: Limit of Secants
- Clip 4: Slope as Ratio
- Clip 5: Main Formula

### Worked Example

Secants and Tangents

Please use the mathlet below to complete the problem.