MHB Domain and range of inverse functions (circular and hyperbolic)

AI Thread Summary
The discussion focuses on the challenges of determining the domain and range of inverse trigonometric functions, particularly $\sin^{-1}(x)$ and $\sec^{-1}(x)$. Participants describe methods for visualizing these functions, such as using the unit circle and flipping graphs over the line $y=x$. There is a consensus that while memorization can be helpful, understanding the underlying principles and practicing can make it easier to recall the domains and ranges. Some express that the process feels tedious, and they seek quicker methods for determining these values. Overall, familiarity and practice are emphasized as key to mastering inverse functions.
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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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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)
 
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