# Horizontal Line Test and One to One Functions | Summary and Q&A

337.5K views
February 11, 2018
by
The Organic Chemistry Tutor
Horizontal Line Test and One to One Functions

## TL;DR

This video explains how to determine if a function has an inverse function by using the horizontal line test.

## Key Insights

• 🫥 A function must pass the horizontal line test to have an inverse function.
• 🫥 One-to-one functions have inverse functions, while functions that intersect a horizontal line multiple times do not.
• 🫥 Parabolic functions and those that intersect a horizontal line at three or more points do not have inverse functions.

## Transcript

consider this function let's use a linear function as our example and let's call it f of x so does f of x have an inverse function determine if f of x have an inverse function you have to show that it's a one-to-one function you have to show that it passes the horizontal line test so if we draw a horizontal line that's a terrible horizontal line if... Read More

### Q: What is the significance of a function passing the horizontal line test?

If a function passes the horizontal line test, it means that it is a one-to-one function, allowing for the existence of an inverse function.

### Q: How can we determine if a function has an inverse function?

By analyzing whether the function intersects a horizontal line more than once, if it does, it is not a one-to-one function, and it does not have an inverse function.

### Q: Can you provide an example of a function that has an inverse function?

Yes, a linear function is an example of a function that has an inverse function. It passes the horizontal line test as it intersects the horizontal line at only one point.

### Q: How does the number of intersection points with a horizontal line affect the existence of an inverse function?

If a function intersects a horizontal line at multiple points, it implies that the function is not one-to-one, and therefore, it does not have an inverse function.

## Summary & Key Takeaways

• To determine if a function has an inverse function, it should pass the horizontal line test and be a one-to-one function.

• If a function intersects a horizontal line more than once, it is not a one-to-one function and does not have an inverse function.

• Examples of functions that do and do not have inverse functions are provided, demonstrating the application of the horizontal line test.