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# C3: Functions - Finding the domain

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1. Is there a way of finding the domain besides sketching the graph of the function?

Thanks
2. (Original post by jessyjellytot14)
Is there a way of finding the domain besides sketching the graph of the function?

Thanks
Work it out using the range.
3. (Original post by RDKGames)
Work it out using the range.
What if the range is ' x ∈ R ' ?
4. (Original post by jessyjellytot14)
Is there a way of finding the domain besides sketching the graph of the function?

Thanks
Think about the function and what is special about it, more specifically what values of x will break the function. Eg f(x) = 1/(x-3) will not like x = 3.

Since lnx won't take negative values (or 0), ln(5x-3) can't take values less than 3/5.

Tanx... etc.
5. (Original post by jessyjellytot14)
What if the range is ' x ∈ R ' ?
That's the domain. Range would be something like

You're probably getting the two confused. Finding the range would vary from function to function, but it's something like a positive quadratic, then you can find the minimum point and it will be everything equal and greater than the y co-ordinate of that min point.
6. (Original post by RDKGames)
That's the domain. Range would be something like

You're probably getting the two confused. Finding the range would vary from function to function, but it's something like a positive quadratic, then you can find the minimum point and it will be everything equal and greater than the y co-ordinate of that min point.
But wouldn't that be the range of the inverse?
7. (Original post by pouii)
But wouldn't that be the range of the inverse?
Domain is the range for the inverse.
Range is the domain for the inverse.

Think of it however you want, she didn't specify any inverses.
8. (Original post by RDKGames)
Domain is the range for the inverse.
Range is the domain for the inverse.

Think of it however you want, she didn't specify any inverses.
Ah ok

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