The Student Room Group
Uni students - Complete our survey >>
Uni students - Complete our survey >>
Uni students - Complete our survey >>

SUPER QUICK MATHS QUESTIOn (C3 Functions)

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..

WIN_20150124_131751.JPG33.0KB
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?
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?
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
Is there a cheat to work out domain and function :frown:
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
starrt.png18.2KB
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)?
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?
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.
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..
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
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! :biggrin: Positive rating given for thanks :smile:

Quick Reply

Related discussions

Latest

Trending

Trending

Articles for you