# Secant lines & average rate of change | Derivatives introduction | AP Calculus AB | Khan Academy | Summary and Q&A

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July 20, 2017
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Secant lines & average rate of change | Derivatives introduction | AP Calculus AB | Khan Academy

## TL;DR

The video discusses the concept of average rate of change, which is the slope of a secant line connecting two points on a curve. This concept is important in calculus as it leads to understanding the derivative.

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### Q: What is the average rate of change of y = x² over the interval from x = 1 to x = 3?

The average rate of change is calculated by finding the change in y over the change in x. In this case, the change in x is 2 and the change in y is 8, resulting in an average rate of change of 4.

### Q: How does the concept of average rate of change relate to the slope of a secant line?

The average rate of change between two points is the same as the slope of the secant line connecting those points on the curve. It provides an approximation of the rate of change over the interval.

### Q: Why is understanding average rate of change important in calculus?

Average rate of change is a foundational concept in calculus because as the points on the interval get closer together, the average rate of change approaches the slope of the tangent line, leading to the concept of instantaneous rate of change or the derivative.

### Q: How does the curve of the function relate to the secant line in terms of rate of change?

The curve of the function represents the actual rate of change at each point, which can vary. The secant line, on the other hand, represents the average rate of change between two points. The curve's rate of change may be different at different points within the interval.

## Summary & Key Takeaways

• The video explains how to calculate the average rate of change of a function over an interval using the example of y = x².

• The concept of average rate of change is illustrated by comparing the slope of the secant line to the curve of the function.

• The video emphasizes that as the points on the interval get closer together, the average rate of change approaches the slope of the tangent line, leading to the concept of instantaneous rate of change or the derivative.