What is the domain of sin(arcsin(x))?

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Homework Help Overview

The discussion revolves around determining the domain of the function sin(arcsin(x)). Participants are exploring the relationship between the arcsine function and the sine function, particularly focusing on the implications of their domains and ranges.

Discussion Character

  • Conceptual clarification, Assumption checking

Approaches and Questions Raised

  • Participants are questioning the domain of arcsin(x) and its implications for sin(arcsin(x)). There is confusion regarding whether the domain of sin should be based on the range of arcsin or the domain of arcsin itself. Some participants are exploring the nature of inverse functions and the restrictions needed for sine to be one-to-one.

Discussion Status

The discussion is active, with participants offering insights into the properties of sine and arcsine. There is recognition of the need to clarify the domains and ranges involved, but no consensus has been reached regarding the interpretation of these functions.

Contextual Notes

Some participants note the importance of understanding the restrictions on the sine function to establish the relationship with arcsine. There is mention of the range of arcsin being [-1, 1] and the implications of this for the overall discussion.

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Homework Statement


I need to find the domain of sin(arcsin(x)). Now I "know" that this is xε(-1,1), but I don't understand why. If the range of arcsin(x) is (-∏/2,∏/2), then shouldn't this be the domain of sin(arcsin(x))?

Help appreciated.
 
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sin (arcsin(x)) means that first arcsin is applied to x, then the result of that is passed on to sin. In what set must x be for this to make sense?
 
Since sine has all real numbers as domain, the domain of this function is the domain of arcsine. Do you understand why its domain is [-1, 1]?
 
HallsofIvy said:
Since sine has all real numbers as domain, the domain of this function is the domain of arcsine. Do you understand why its domain is [-1, 1]?

I understand why the domain of arcsin is [1,-1]. But if sine is the inverse of arcsine, shouldn't the domain of sine be the range of arcsine? I thought that was the rule where inverse functions are concerned.
 
11thHeaven said:
I understand why the domain of arcsin is [1,-1]. But if sine is the inverse of arcsine, shouldn't the domain of sine be the range of arcsine? I thought that was the rule where inverse functions are concerned.
The sine function is not a one-to-one function, so technically, there is no function which is the inverse of sine function.

So, where do we get the arcsine function from? If we restrict the sine function to a domain of [-π/2, π/2], then that restricted sine function is one-to-one. (By the Way: The range of this restricted sine function is [-1, 1], the same as for the "unrestricted" sine function.) The arcsine function is the inverse of this restricted sine function.

As it turns out, sin(arcsin(x)) has the same domain and range regardless of which of these sine functions is used.
 

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