
# 1: Understanding the Derivative

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• 1.1: How do we Measure Velocity?
The average velocity on [a,b] can be viewed geometrically as the slope of the line between the points (a,s(a)) and (b,s(b)) on the graph of y=s(t). The instantaneous velocity of a moving object at a fixed time is estimated by considering average velocities on shorter and shorter time intervals that contain the instant of interest
• 1.2: The Notion of Limit
Limits enable us to examine trends in function behavior near a specific point. In particular, taking a limit at a given point asks if the function values nearby tend to approach a particular fixed value.
• 1.3: The Derivative of a Function at a Point
An idea that sits at the foundations of calculus is the instantaneous rate of change of a function. This rate of change is always considered with respect to change in the input variable, often at a particular fixed input value. This is a generalization of the notion of instantaneous velocity and essentially allows us to consider the question “how do we measure how fast a particular function is changing at a given point?”
• 1.4: The Derivative Function
The limit definition of the derivative produces a value for each x at which the derivative is defined, and this leads to a new function whose formula is y = f'(x). Hence we talk both about a given function f and its derivative f'. It is especially important to note that taking the derivative is a process that starts with a given function (f) and produces a new, related function (f').
• 1.5: Interpretating, Estimating, and Using the Derivative
Regardless of the context of a given function $$y = f (x)$$, the derivative always measures the instantaneous rate of change of the output variable with respect to the input variable. The units on the derivative function $$y = f'(x)$$ are units of $$f$$ per unit of $$x$$. Again, this measures how fast the output of the function $$f$$ changes when the input of the function changes.
• 1.6: The Second Derivative
A differentiable function f is increasing at a point or on an interval whenever its first derivative is positive, and decreasing whenever its first derivative is negative. By taking the derivative of the derivative of a function f', we arrive at the second derivative, f''. The second derivative measures the instantaneous rate of change of the first derivative, and thus the sign of the second derivative tells us whether or not the slope of the tangent line to f is increasing or decreasing.
• 1.7: Limits, Continuity, and Differentiability
A function f has limit as x → a if and only if f has a left-hand limit at x = a, has a right-hand limit at x = a, and the left- and right-hand limits are equal. A function f is continuous at x = a whenever f (a) is defined, f has a limit as x → a, and the value of the limit and the value of the function agree. This guarantees that there is not a hole or jump in the graph of f at x = a. A function f is differentiable at x = a whenever f' (a) exists.
• 1.8: The Tangent Line Approximation
The principle of local linearity tells us that if we zoom in on a point where a function y = f (x) is differentiable, the function should become indistinguishable from its tangent line. That is, a differentiable function looks linear when viewed up close.
• 1.E: Understanding the Derivative (Exercises)
These are homework exercises to accompany Chapter 1 of Boelkins et al. "Active Calculus" Textmap.