Domain and range of inverse functions (circular and hyperbolic)

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SUMMARY

The discussion focuses on the domain and range of inverse trigonometric functions, specifically $\sin^{-1}(x)$ and $\sec^{-1}(x)$. Participants emphasize the importance of visualizing the sine function's graph and its range, which is restricted to $[-\frac{\pi}{2}, \frac{\pi}{2}]$ for invertibility. Techniques such as flipping the graph over the line $y=x$ and marking key points are suggested for better understanding. The conversation highlights that while memorization can be tedious, consistent practice aids retention of these concepts.

PREREQUISITES
  • Understanding of trigonometric functions, specifically sine and secant.
  • Familiarity with graphing techniques and transformations.
  • Knowledge of the unit circle and its significance in trigonometry.
  • Basic concepts of inverse functions and their properties.
NEXT STEPS
  • Study the properties of inverse trigonometric functions, including their domains and ranges.
  • Learn how to graph inverse functions by reflecting over the line $y=x$.
  • Explore the unit circle in detail to enhance understanding of angle measures and their corresponding sine and cosine values.
  • Practice deriving the domains and ranges of other inverse functions, such as $\tan^{-1}(x)$ and $\cot^{-1}(x)$.
USEFUL FOR

Students, educators, and anyone studying trigonometry who seeks to deepen their understanding of inverse functions and their graphical representations.

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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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