This document discusses tangent lines and provides a refresher on relevant pre-calculus and calculus concepts. It defines a tangent line as one that touches a curve at exactly one point and notes that the slope of a tangent line at any point can be found using the first derivative. Formulas for the slope-intercept and point-slope forms of a line are presented, along with properties that parallel lines have the same slope while perpendicular lines have slopes that multiply to -1.