You are Here: Home >< Maths

# IS THIS GRAPH RIGHT? (Taking into account domain )

Announcements Posted on
Would YOU be put off a uni with a high crime rate? First 50 to have their say get a £5 Amazon voucher! 27-10-2016
1. (Original post by BobBobson)
4x-x^2 does go through 4 normally, however in your OP, you said the domain for it is 2<= x <= 4, so your x co-ordinates should stop dead at 4. Any number past 4 isn't in the domain of 4x-x^2, and thus shouldn't be plotted.
I know what you mean but the way I drew the graph it's passing through 4 and not touching 5
2. (Original post by Jane122)
I know what you mean but the way I drew the graph it's passing through 4 and not touching 5
Yeah that's wrong as well, because now your function isn't even valid. For a function to be a valid, each x value within the domain can only be paired with either 0 or 1 y value. For x=4, it has infinite y values, since the line is going straight down.
3. (Original post by BobBobson)
Yeah that's wrong as well, because now your function isn't even valid. For a function to be a valid, each x value within the domain can only be paired with either 0 or 1 y value. For x=4, it has infinite y values, since the line is going straight down.
But it's not a 1 to 1 function..
4. (Original post by Jane122)
But it's not a 1 to 1 function..
It doesn't have to be. If an x value has more than one y value, it's not a valid function.
5. (Original post by BobBobson)
It doesn't have to be. If an x value has more than one y value, it's not a valid function.
Like this?!!! Even if it goes through 4 isn't it still less than equal to 4 since it's not touching 5 and so on
6. (Original post by Jane122)
Like this?!!! Even if it goes through 4 isn't it still less than equal to 4 since it's not touching 5 and so on
No, because if it goes through 4, it means it's touching 4.1 or 4.0000000001, which is greater than 4 and not <= 4. It must stop exactly dead at 4
7. (Original post by BobBobson)
No, because if it goes through 4, it means it's touching 4.1 or 4.0000000001, which is greater than 4 and not <= 4. It must stop exactly dead at 4
OHHHHH!!!!! OMG I finally understand LOL thank you so much!!!! I could kiss you.this stumped me for 1hr
8. You're welcome
9. Always try to be accurate, it's good practice.

## Register

Thanks for posting! You just need to create an account in order to submit the post
1. this can't be left blank
2. this can't be left blank
3. this can't be left blank

6 characters or longer with both numbers and letters is safer

4. this can't be left empty
1. Oops, you need to agree to our Ts&Cs to register

Updated: October 2, 2016
TSR Support Team

We have a brilliant team of more than 60 Support Team members looking after discussions on The Student Room, helping to make it a fun, safe and useful place to hang out.

This forum is supported by:
Today on TSR

### University open days

Is it worth going? Find out here

Poll
Useful resources

### Maths Forum posting guidelines

Not sure where to post? Read here first

### How to use LaTex

Writing equations the easy way

### Study habits of A* students

Top tips from students who have already aced their exams