Domain and range of inverse functions (circular and hyperbolic)

In summary, the conversation discusses the challenges of determining the domain and range of inverse trigonometric functions, specifically using $\sin^{-1}\left({x}\right)$ and $\sec^{-1}\left({x}\right)$ as examples. The process involves drawing out the original function and restricting it to make it invertible, which can be achieved by flipping the graph over the line $y=x$. The conversation also mentions alternative methods and the tediousness of memorizing the domains and ranges of inverse functions.
  • #1
Dethrone
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I've always been having trouble with the domain and range of inverse trigonometric functions. For example, let's start with an easy one: $\sin^{-1}\left({x}\right)$

Process: First, I draw out the function of $\sin\left({x}\right)$. Then I look at its range and attempt to restrict it so that it is invertible, which is from $\frac{-\pi}{2}$ to $\frac{\pi}{2}$. Now to draw the graph, I have to rotate it by the axis $y=x$...I can't seem to visualize how to do that...Do I turn my page sideways?

Let's try another one: $\sec^{-1}\left({x}\right)$
Drawing $\sec\left({x}\right)$ first, I look at its asymptotes which are when $\cos\left({x}\right)$ is equal to $0$ on... Does someone actually go through all this work to find the domain and range of $\sec^{-1}\left({x}\right)$? Or do they have it memorized?

This seems very tedious and a lot of work to know the domain and range of inverse functions. Is there a quicker way? (Wondering)
 
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  • #2
Rido12 said:
I've always been having trouble with the domain and range of inverse trigonometric functions. For example, let's start with an easy one: $\sin^{-1}\left({x}\right)$

Process: First, I draw out the function of $\sin\left({x}\right)$. Then I look at its range and attempt to restrict it so that it is invertible, which is from $\frac{-\pi}{2}$ to $\frac{\pi}{2}$.

Yep. That's a way to do it.

I usually visualize the unit circle in my mind and consider the range of the sine and the corresponding angles "that make sense".
Now to draw the graph, I have to rotate it by the axis $y=x$...I can't seem to visualize how to do that...Do I turn my page sideways?

Not rotate - flip.
That is, keep the page fixed at bottom-left and top-right, and flip it.

Or you start with the sine graph and the line $y=x$ and then mirror a couple of key points in the line.

Alternatively you can start by marking the horizontal axis with -1 and +1, and mark a couple of points to help draw the graph.
Let's try another one: $\sec^{-1}\left({x}\right)$
Drawing $\sec\left({x}\right)$ first, I look at its asymptotes which are when $\cos\left({x}\right)$ is equal to $0$ on... Does someone actually go through all this work to find the domain and range of $\sec^{-1}\left({x}\right)$? Or do they have it memorized?

I'm afraid I never use $\sec$, so I'm usually not interested in its domain or range.
If someone asks, I just have to look it up, or figure it out again.
I usually use $\frac{1}{\cos x}$ instead.
This seems very tedious and a lot of work to know the domain and range of inverse functions. Is there a quicker way? (Wondering)

With practice they tend to stick to mind. But it's not too bad if you forget. You just need a quick and reliable way to deduce them. (Sweating)
 

FAQ: Domain and range of inverse functions (circular and hyperbolic)

What is the definition of a domain and range?

The domain of a function is the set of all possible inputs or x-values for which the function is defined. The range is the set of all possible outputs or y-values that the function can produce.

How do you find the domain and range of inverse functions?

To find the domain and range of inverse functions, you can switch the x and y values of the original function to create the inverse function. The domain of the inverse function will be the range of the original function, and the range of the inverse function will be the domain of the original function.

What is a circular inverse function?

A circular inverse function is a function that is the inverse of a circular function, such as sine, cosine, or tangent. This type of inverse function is used to solve for the angle measure given the ratio of sides in a right triangle.

What is a hyperbolic inverse function?

A hyperbolic inverse function is a function that is the inverse of a hyperbolic function, such as sinh, cosh, or tanh. These types of inverse functions are used in calculus and in solving problems related to hyperbolic geometry.

Why is it important to understand the domain and range of inverse functions?

Understanding the domain and range of inverse functions is important because it allows us to determine the validity of the inverse function and to solve for unknown values. It also helps us to identify the behavior and characteristics of a function and its inverse, which is crucial in many applications of mathematics and science.

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