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C3 range and domain watch

1. How do you work out the range and domain especially when it specifies in the question that x>1 (for example).

2X+3/X-1 x is any real number x>1
How would i find the range of this function?
2. The way I do is think of it as:

Range - Output - On y axis if on graph

Domain - Input - X axis

For that function, f(x) can be infinitely large as x tends to 1, and will tend to 2x/x, so 2.
This would lead me to think that the range is f(x) >2 and f(x) is real - unless i've misunderstood the function.
3. (Original post by MIKE ESSIEN IS QUITE SICK)
How do you work out the range and domain especially when it specifies in the question that x>1 (for example).

2X+3/X-1 x is any real number x>1
How would i find the range of this function?
the range has got to be not equal to 1 (other wise the bottom part will be zero)
4. (Original post by unamed)
the range has got to be not equal to 1 (other wise the bottom part will be zero)
5. (Original post by Samw1se)
I am. sorry, I think my mind temporarily went into overload.
6. so say for example a question was what is the domain of 5x+9/2x+3 would the domain be x>-1.5
7. Not necessarily, it would probably be x doesn't equal 1.5. There could be values of x below that.
8. (Original post by Samw1se)
Not necessarily, it would probably be x doesn't equal 1.5. There could be values of x below that.
So how do you know when to make it < or >??
What can you use to work it out?
9. (Original post by Merk that Sike of a Mike)
So how do you know when to make it < or >??
What can you use to work it out?
It can be both.

x can be any number, except -1.5
10. (Original post by Merk that Sike of a Mike)
So how do you know when to make it < or >??
What can you use to work it out?
A question will usually either:

(i) Give you the function and domain, and ask you to work out the range.

or

(ii) Give you the function and range, and ask you to work out the domain.

If you just get a function - try to exclude values that are impossible. For example, if f(x) = x^2 and the domain is all real values of x, then the range must be f(x) >= 0, since there is no real value of x that will produce a value of f(x) below 0.
11. (Original post by Samw1se)
A question will usually either:

(i) Give you the function and domain, and ask you to work out the range.

or

(ii) Give you the function and range, and ask you to work out the domain.

If you just get a function - try to exclude values that are impossible. For example, if f(x) = x^2 and the domain is all real values of x, then the range must be f(x) >= 0, since there is no real value of x that will produce a value of f(x) below 0.
Just a minor correction but f(x) ≥ 0 as x can be 0 rendering f(x) to be 0.
12. (Original post by AnonyMatt)
It can be both.

x can be any number, except -1.5
Yes, you jus right
13. (Original post by big-bang-theory)
Just a minor correction but f(x) ≥ 0 as x can be 0 rendering f(x) to be 0.
I did say that, I just used >= instead of ≥.
14. (Original post by Samw1se)
I did say that, I just used >= instead of ≥.
So you did sorry, 4 hours of C3 revision today has apparently dulled my basic reading skills...
15. why is the demain of x^2+3 x=>2

(x any real number x=>7)
i thought the demain would be x=>7
16. (Original post by big-bang-theory)
So you did sorry, 4 hours of C3 revision today has apparently dulled my basic reading skills...
Feeling the same!
17. (Original post by MIKE ESSIEN IS QUITE SICK)
why is the demain of x^2+3 x=>2

(x any real number x=>7)
i thought the demain would be x=>7
I'm sorry, but I don't quite understand what you're asking?

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