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Defining Average and Instantaneous Rates of Change at a Point Chapter Notes | Calculus AB - Grade 9 PDF Download

Welcome back to AP Calculus with Fiveable! After covering Limits and Continuity in Unit 1, we are now diving into Unit 2: Differentiation - Definition and Basic Derivative Rules. Our focus in this section is to understand the concepts of average and instantaneous rates of change at a point. Let’s get into it!

Average Rate of Change


The average rate of change is often used to represent average speed, average velocity, or average growth rate. In calculus, understanding rates of change is crucial, similar to the concept of slope in algebra.

Defining Average and Instantaneous Rates of Change at a Point Chapter Notes | Calculus AB - Grade 9

Formula to calculate a slope by taking 2 points.
For any two points on a continuous function f(x) within the interval [a, b], the average rate of change can be expressed as:
Defining Average and Instantaneous Rates of Change at a Point Chapter Notes | Calculus AB - Grade 9

This is also the slope of the secant line between any two points.

Instantaneous Rate of Change


While the average rate of change informs us how a function behaves over an interval, the instantaneous rate of change tells us the rate of change at an exact point. In calculus, we express this using the derivative.
The instantaneous rate of change of a function f(x) at a specific point x = c is denoted as f′(x) and is given by the limit:
Defining Average and Instantaneous Rates of Change at a Point Chapter Notes | Calculus AB - Grade 9
This limit represents the slope of the tangent line to the graph of f(x) at the point (c,f(c)). In other words, it tells us how fast the function is changing precisely at the point x = c.

️‍Practice Problems


Let’s work on a few questions to get the concepts down! Here are a few steps you can follow when approaching problems that ask you to solve for average rate of change or instantaneous rate of change:

  • ️ Identify the function and the interval.
  • Apply the formula for the rate of change you are solving for, either average or instantaneous.
  • Substitute the values and solve.

1) Solving Average Rate of Change


Consider the function f(x) = x2 over the interval [1, 3]. Calculate the average rate of change.
Step 1: Identify the function and the interval.
Defining Average and Instantaneous Rates of Change at a Point Chapter Notes | Calculus AB - Grade 9

Step 2: Apply the formula for an average rate of change.
Average Rate of Change:Defining Average and Instantaneous Rates of Change at a Point Chapter Notes | Calculus AB - Grade 9

Step 3: Substitute the values and solve.
Average Rate of Change: Defining Average and Instantaneous Rates of Change at a Point Chapter Notes | Calculus AB - Grade 9

2) Solving Instantaneous Rate of Change

Consider the function f(x) = x2. Find the instantaneous rate of change at x = 2.

Step 1: Identify the function and the point.

Defining Average and Instantaneous Rates of Change at a Point Chapter Notes | Calculus AB - Grade 9

Defining Average and Instantaneous Rates of Change at a Point Chapter Notes | Calculus AB - Grade 9

Step 2: Apply the formula for the instantaneous rate of change.
Instantaneous Rate of Change:

Defining Average and Instantaneous Rates of Change at a Point Chapter Notes | Calculus AB - Grade 9

Step 3: Substitute the values and solve.
Instantaneous Rate of Change:

Defining Average and Instantaneous Rates of Change at a Point Chapter Notes | Calculus AB - Grade 9

Question for Chapter Notes: Defining Average and Instantaneous Rates of Change at a Point
Try yourself:
What does the instantaneous rate of change represent?
View Solution

Summing it Up

You made it to the end of the first topic in unit 2! Great work. Here’s a quick table displaying the differences between average and instantaneous rates of change for you to take with you throughout the unit.

Defining Average and Instantaneous Rates of Change at a Point Chapter Notes | Calculus AB - Grade 9

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FAQs on Defining Average and Instantaneous Rates of Change at a Point Chapter Notes - Calculus AB - Grade 9

1. What is the average rate of change in a function?
Ans. The average rate of change of a function over an interval [a, b] is the difference in the function values at the endpoints of the interval divided by the difference in the input values. It can be calculated using the formula: (f(b) - f(a)) / (b - a).
2. How do you calculate the instantaneous rate of change at a specific point?
Ans. The instantaneous rate of change of a function at a specific point is found using the derivative of the function at that point. It is represented as f'(a) and can be calculated using the limit: lim (h -> 0) [f(a + h) - f(a)] / h.
3. What is the difference between average rate of change and instantaneous rate of change?
Ans. The average rate of change measures how a function behaves over a specific interval, while the instantaneous rate of change measures how the function behaves at a precise point. The average rate corresponds to the slope of the secant line, whereas the instantaneous rate corresponds to the slope of the tangent line at that point.
4. Can the average rate of change be negative?
Ans. Yes, the average rate of change can be negative if the function decreases over the interval [a, b]. This indicates that the output of the function is decreasing as the input increases.
5. Why is understanding rates of change important in calculus?
Ans. Understanding rates of change is crucial in calculus because it helps describe how functions behave, allowing us to analyze motion, growth, and other changes in various fields such as physics, economics, and biology. Rates of change provide insights into trends and can be used to make predictions.
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