Applications of Derivatives, Extreme Values of Functions, and the Mean Value Theorem¶ Applications of Derivatives¶ Rate measure: \(dy/dx\) = \(\Delta y/\Delta x\) = \(f'(x)\) Errors and approximations. Increasing and decreasing functions. Maxima and minima. Tangent lines and normal lines. Roles theorem¶ If \(f\) is continuous on \([a,b]\) and differentiable on \((a,b)\), and \(f(a) = f(b)\), then there exists a number \(c\) in \((a,b)\) such that \(f'(c) = 0\) (the slope of the tangent line is zero).