This document discusses implicit differentiation and finding the tangent line to a circle implicitly defined by an equation. It provides an example of using implicit differentiation to find the slope of the tangent line to the circle x^2 + y^2 = 25 at the point (3,4). The steps are to differentiate both sides of the equation with respect to x, solve for dy/dx, and plug in the x and y values of the point to find the slope of the tangent line.