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# SUPER QUICK MATHS QUESTIOn (C3 Functions) watch

1. For part b I've got gf = 3/8x-3 but then the questions asks for it's domain and I don't know how to do that..

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2. (Original post by creativebuzz)
For part b I've got gf = 3/8x-3 but then the questions asks for it's domain and I don't know how to do that..

Well, as x is on the bottom of the fraction, think of the cases where the function would return an undefined number?
3. (Original post by sarcasmrules)
Well, as x is on the bottom of the fraction, think of the cases where the function would return an undefined number?
It would be undefined if 8x-3=0 so x=3/8

But why are we trying to find where the function would be undefined?
4. (Original post by creativebuzz)
It would be undefined if 8x-3=0 so x=3/8

But why are we trying to find where the function would be undefined?
Well domain is all the values of x a function can take
When x=3/8 we get 0 for the denominator which we can't do.

When you have a fraction the domain is every x value apart from the one that makes it 0
So in this case x is an element of the real numbers , x cannot be 3/8
5. Is there a cheat to work out domain and function
6. (Original post by Super199)
Well domain is all the values of x a function can take
When x=3/8 we get 0 for the denominator which we can't do.

When you have a fraction the domain is every x value apart from the one that makes it 0
So in this case x is an element of the real numbers , x cannot be 3/8
Ah okay, so where did I go wrong here in part b:

y = x/x -2

therefore, horizontal asymptote: x=2
vertical asymptote: y= 2

so the range is every value except x = 2
and the domain is every value except y = 1
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7. (Original post by creativebuzz)
Ah okay, so where did I go wrong here in part b:

y = x/x -2

therefore, horizontal asymptote: x=2
vertical asymptote: y= 2

so the range is every value except x = 2
and the domain is every value except y = 1
Do you know the relationship between the domain of f(x) and the range of f^-1(x)?
8. (Original post by Super199)
Do you know the relationship between the domain of f(x) and the range of f^-1(x)?
the domain of f(x) = the range of f^-1(x)

the range of f(x) = the domain of f^-1(x)

so if the domain of f(x) is every value except x =2, then the range of f^-1(x) is every value except x =2

is that correct?
9. (Original post by creativebuzz)
the domain of f(x) = the range of f^-1(x)

the range of f(x) = the domain of f^-1(x)

so if the domain of f(x) is every value except x =2, then the range of f^-1(x) is every value except x =2

is that correct?
Y is an element of the real y cannot be 2. Since it's range and not domain so you use y.
10. (Original post by Super199)
Y is an element of the real y cannot be 2. Since it's range and not domain so you use y.
I don't understand what you're trying to say..
11. (Original post by creativebuzz)
I don't understand what you're trying to say..
You use y instead of x when it's range ( I think). So every y value apart from 2
12. (Original post by Super199)
You use y instead of x when it's range ( I think). So every y value apart from 2

Ah yes I see what you mean! I understand it now! Positive rating given for thanks

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