You are Here: Home >< A-levels

# Quadratic question help

1. A line has equation y = 2x − 7 and a curve has equation y = x
2 − 4x + c, where c is a constant. Find
the set of possible values of c for which the line does not intersect the curve.
2. (Original post by Revision 99)
A line has equation y = 2x − 7 and a curve has equation y = x
2 − 4x + c, where c is a constant. Find
the set of possible values of c for which the line does not intersect the curve.
Knowing that they never intersect, how can you use quadratic equations to solve this question?
3. (Original post by SeanFM)
Knowing that they never intersect, how can you use quadratic equations to solve this question?
Okay, but then how are we supposed to solve, atleast give a starting point with an explanation
4. (Original post by Revision 99)
Okay, but then how are we supposed to solve, atleast give a starting point with an explanation
When you have the equation of the curve, are you sure it was y=x, not perhaps y=x^2
5. (Original post by Revision 99)
Okay, but then how are we supposed to solve, atleast give a starting point with an explanation
That was one, I think encouraging people to think for themselves and giving subtle prompts makes them learn the most from the question

If two curves intersect, what can you say about the curve that you get when you take one away from the other? (Think about the points of intersection originally, then what happens when you take one away from the other, specifically at the points of intersection)

Then think about what happens when they never intersect and how you can use quadratic equations to solve your question using the equation f(x) - g(x), where f and g are the two original equations.

If you want an example, say you had y = x^2 - 5 and y = 4 as two equations. They have two points of intersection, so when you take one away from the other, at the points intersection the y co-ordinate is 0, so the equation has two distinct solutions, which can be found using the quadratic equation. If there were no intersections originally.. would there be any points where y = 0? (i.e the difference between two y values for both curves for each x value)

## 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
your full birthday is required
1. Oops, you need to agree to our Ts&Cs to register

Updated: October 1, 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

### Five things other students are thinking right now

The latest news from our 'Grow your Grades' bloggers

### Can't make her orgasm

Poll
Help with your A-levels

## All the essentials

### Student life: what to expect

What it's really like going to uni

### Essay expert

Learn to write like a pro with our ultimate essay guide.

### Uni match

Our tool will help you find the perfect course for you

### Create a study plan

Get your head around what you need to do and when with the study planner tool.

### Resources by subject

Everything from mind maps to class notes.

### Degrees without fees

Discover more about degree-level apprenticeships.

### Study tips from A* students

Students who got top grades in their A-levels share their secrets

## Study help links and info

Can you help? Study help unanswered threadsRules and posting guidelines

### HEAR

Find out how a Higher Education Achievement Report can help you prove your achievements.

## 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.