Turn on thread page Beta
 You are Here: Home >< Maths

# Completing Square watch

1. So say I had this:
x^2 + 8x +3
(x + 4)^2 -16 +3
(x + 4)^2 -13
Therefore, the minimum point is (-4,-13)

What if the coefficient was a minus:
-3x^2 + 5x + 5

What would be the minimum points then?
2. = -3(x-5/6)^2 + 85/12
Minimum point = (5/6, 85/12)
3. (Original post by Neevan)
= -3(x-5/6)^2 + 85/12
Minimum point = (5/6, 85/12)

Thank you so much!!! So regardless of the minus, the x coordinate of the minimum point will be positive and not timesed by 3? It's basically never affected by the coefficient right...oh and the y as well for that matter?
4. (Original post by Nieveee)
So say I had this:
x^2 + 8x +3
(x + 4)^2 -16 +3
(x + 4)^2 -13
Therefore, the minimum point is (-4,-13)

What if the coefficient was a minus:
-3x^2 + 5x + 5

What would be the minimum points then?
It won't be a minimum though will it?

What shape is a quadratic with a negative x^2 coefficient?
5. (Original post by Muttley79)
It won't be a minimum though will it?

What shape is a quadratic with a negative x^2 coefficient?
Ahhh, it'd be a maximum right, considering it's the other way round?
6. (Original post by Nieveee)
Ahhh, it'd be a maximum right, considering it's the other way round?
Indeed
7. sorry about that
8. (Original post by Muttley79)
Indeed
Oh, so would I be right in saying the maximum of this is, for example:

-2(x-2)^2 + 18
= (2,18)

and this:
4(x-3)^2 + 23
= (3, 23) is the minimum point?
9. (Original post by Neevan)
sorry about that
No problem!
10. (Original post by Nieveee)
Oh, so would I be right in saying the maximum of this is, for example:

-2(x-2)^2 + 18
= (2,18)

and this:
4(x-3)^2 + 23
= (3, 23) is the minimum point?
Yes - remember you can always check by differentiating and putting dy/dx =0 if you have time.

Reply
Submit reply
Turn on thread page Beta

### Related university courses

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:
Updated: May 12, 2015
Today on TSR

### Edexcel C4 Maths Unofficial Markscheme

Find out how you've done here

### 2,706

students online now

Exam discussions

Poll
Useful resources

## Make your revision easier

### Maths Forum posting guidelines

Not sure where to post? Read the updated guidelines here

### How to use LaTex

Writing equations the easy way

### Study habits of A* students

Top tips from students who have already aced their exams

Can you help? Study help unanswered threads

## Groups associated with this forum:

View associated groups

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

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