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# Q on domains watch

1. For part b, I thought the domain of f o f is all real numbers except -5 but it states that the right answer is all real numbers except -5 and 2.

I realised that if x = 2, then f o f = 3 and I can see where this is going but I don't have as clear an idea of the concept in play here as I'd like. Could someone explain this to me in detail, please?

EDIT : Is this it?

If the domain included x = 2, then . But if , then, But this is not possible since cannot take the value 3 since 3 is not a part of the domain of

Thank you!

Sid
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2. (Original post by Sidhant Shivram)

For part b, I thought the domain of f o f is all real numbers except -5 but it states that the right answer is all real numbers except -5 and 2.

I realised that if x = 2, then f o f = 3 and I can see where this is going but I don't have as clear an idea of the concept in play here as I'd like. Could someone explain this to me in detail, please?

Thank you!

Sid

x=2 cannot go in the first "stage"
x=-5 cannot go in the second stage.
You can see this in the denominator or set the function = 2 gives -5
3. Okay. Got it.Thanks!
4. (Original post by Sidhant Shivram)
Okay. Got it.Thanks!
no worries

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Updated: December 26, 2014
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