You are Here: Home >< Maths

# a level maths C1

Announcements Posted on
TSR's new app is coming! Sign up here to try it first >> 17-10-2016
1. Help please someone tell me how to do inequalities and also tell me how you know the sign is < or > . For example, x^2 -11x+24<0, why is the answer 3<x<8 and how do you do it please !!!!!! anwer
2. (Original post by Mr revision)
Help please someone tell me how to do inequalities and also tell me how you know the sign is < or > . For example, x^2 -11x+24<0, why is the answer 3<x<8 and how do you do it please !!!!!! anwer
You sketch the graph and look for the points where y < 0 or y> 0 etc.

For what values of x is the y value less than 0?
3. (Original post by Mr revision)
Help please someone tell me how to do inequalities and also tell me how you know the sign is < or > . For example, x^2 -11x+24<0, why is the answer 3<x<8 and how do you do it please !!!!!! anwer
You have to find the critical values.

factorises to

draw that curve and look for the region where y is less than 0.
4. (Original post by SeanFM)
You sketch the graph and look for the points where y < 0 or y> 0 etc.

For what values of x is the y value less than 0?
Spoiler:
Show
i was going to answer that
Spoiler:
Show
you always hack on maths threads
Spoiler:
Show
jokes
Spoiler:
Show
no i wasn't
5. (Original post by Mr revision)
Help please someone tell me how to do inequalities and also tell me how you know the sign is < or > . For example, x^2 -11x+24<0, why is the answer 3<x<8 and how do you do it please !!!!!! anwer
first, set and solve for x to find critical values.

when you do this youll get x = 3 or x = 8.

From here you need to work out whether the curve is less than 0 for 3<x<8 or x<3 U x>8. To do this you have two choices;

Sketch it - you can see that the quadratic has a y intercept of 24 so you know three points on the curve are (0,24), (3,0) and (8,0). You also know this quadratic has a U shape so a quick sketch will tell you that for values 3 < x < 8.

Or you can sub in some values - sub in x = 0, x = 5 and x = 10 for example and youll see that f(0) >0, f(5) < 0 and f(10) > 0 therefore the function is <0 for values 3<x<8
6. Thank you all but how do you look for the region where y>0 or y<0
7. (Original post by NotNotBatman)
You have to find the critical values.

factorises to

draw that curve and look for the region where y is less than 0.
Thanks but how do you look for the region where y is less than 0
8. (Original post by Mr revision)
Thanks but how do you look for the region where y is less than 0
All the points of the curve below the x axis. If you look at the graph SeanFM posted, y=0 on the x axis, so at x=3 and x=8, anything below that is where y<0 and anything above is where y>0.

## 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 4, 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

### How does exam reform affect you?

From GCSE to A level, it's all changing

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

## Groups associated with this forum:

View associated groups
Study resources

The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE

Reputation gems: You get these gems as you gain rep from other members for making good contributions and giving helpful advice.