DOMAIN OF x^2-1

OP

Original post by SeanFM

The domain is the x values for which y values exist. Y values exist for every x value on that function.

So it's always xer? I still don't get where I went wrong on that question like is it cos the domains not restricted?

Reply 6

OP

Original post by Prince David

The domain of the function y=x^2-1 constitutes the values of x, for which y has a real value, the domain is therefore = -infinity < x < infinity

So it's always xer? Wb -1<f(x)<1

Reply 7

Original post by Jane122

So it's always xer? Wb -1<f(x)<1

For this function the domain is xER since any value of x gives a valid value for the function.
*You can choose to restrict a domain to a specific set of values (for example if you wish to restrict it to a 1 to 1 function it could be x > 0. The range of a function is the possible values for f(x) given the domain (possible x values), in this case f(x) is greater than or equal to -1
You could be asked to solve when the function is < 0 i.e. -1<f(x)<1

Posted from TSR Mobile

(edited 7 years ago)

Reply 8

sindyscape62

10

Original post by Jane122

So it's always xer? I still don't get where I went wrong on that question like is it cos the domains not restricted?

The domain is not always all real values, it's just that for that particular equation the domain is not restricted. To work out the domain try to find values of x that can't be put into the equation, if there are some then the domain is restricted.

For example if you had

y=\sqrt x

then the domain is restricted to

x \geq 0

because you won't get a real answer if you input a negative value of x.

Reply 9

alow

19

Original post by Jane122

So it's always xer? I still don't get where I went wrong on that question like is it cos the domains not restricted?

wtf is an xer

x \in \mathbb{R}

\LaTeX

is your friend.

Reply 10

OP

Original post by sindyscape62

The domain is not always all real values, it's just that for that particular equation the domain is not restricted. To work out the domain try to find values of x that can't be put into the equation, if there are some then the domain is restricted.

For example if you had

y=\sqrt x

then the domain is restricted to

x \geq 0

because you won't get a real answer if you input a negative value of x.

I drew the graph of x^2-1 and it cuts the x axis at 1 and -1. So wouldn't the domain be between 1 and -1? Why is it xer?

Reply 11

Original post by Jane122

I drew the graph of x^2-1 and it cuts the x axis at 1 and -1. So wouldn't the domain be between 1 and -1? Why is it xer?

The domain has nothing to do with when f(x) < 0.
As people have said a few time in this thread, the domain of a function is the the set of values that x is allowed to be.

(edited 7 years ago)

Reply 12

OP

Original post by gdunne42

The domain has nothing to do with when f(x) < 0.
As people have said a few time in this thread, the domain of a function is the the set of values that x is allowed to be.

I'm sorry but I'm really confused despite drawing the graph I can't figure out the domanin. I want someone to clear up my understanding as to why the domain is xer and not between -1 and 1.

Reply 13

OP

Original post by gdunne42

The domain has nothing to do with when f(x) < 0.
As people have said a few time in this thread, the domain of a function is the the set of values that x is allowed to be.

Also with the graph of - root over x-3 whys the range < less than equal to 0 ?

Reply 14

Kevin De Bruyne

Original post by Jane122

I'm sorry but I'm really confused despite drawing the graph I can't figure out the domanin. I want someone to clear up my understanding as to why the domain is xer and not between -1 and 1.

You are not clear on what a domain is - that's fine. People have defined it in the thread but as you are still stuck I would suggest asking your teacher about it going over the material in the textbook about it.

(edited 7 years ago)

Reply 15

Original post by Jane122

I'm sorry but I'm really confused despite drawing the graph I can't figure out the domanin. I want someone to clear up my understanding as to why the domain is xer and not between -1 and 1.

OK, one last time.
Where it crosses the x axis has NOTHING to do with the domain of the function.
Can you enter x=2 into your function and generate a result for f(x) ?
x=10 ? x=-5 ?
Any positive or negative (real) value you could possibly choose can be put into your function and generate a value for f(x) therefore "x can be any real number" is the domain of this function.

(edited 7 years ago)

Reply 16