You are Here: Home >< Maths

Can't seem to be able to complete the square for this?

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. Part b) specifically.

I did 2x^2 + 8x + 3 = (x+2)^2 - 4 + (3/2)
= (x+2)^2 - (5/2)

That is apparently incorrect.
The answer is 2(x + 2)^2 - 5

I don't understand how that was achieved though. I see it like this:
2(x^2 +4x + (3/2))

2((x + 2)^2 - 4 + (3/2)), which is practically the same?
How else do I do this?

And can anyone explain to me why 2(x^2 +4x + (3/2)) is the same as just x^2 + 4x + (3/2) ? I mean surely they're not equal, the first one is x2 the second one, but I was taught that doing so to an equation is fine?
2. (Original post by frostyy)
...
Do you agree that you can write ? i.e: you can pull a factor of 2 out?

So for example, when you're given you can then pull the common factor of 2 out to get you .

Then you complete the square on the inside: .

Which step don't you understand in here?
3. Try arranging 2x^2 + 8x into p(x+q)^2

2(x+2)^2 which is equal to 2(x^2 + 4x + 4).

If you expand that it becomes 2x^2 + 8x + 8, then you have to find what r is equal to to make +8 equal to +3
4. (Original post by Zacken)
Do you agree that you can write ? i.e: you can pull a factor of 2 out?

So for example, when you're given you can then pull the common factor of 2 out to get you .

Then you complete the square on the inside: .

Which step don't you understand in here?
Oh right, sorry. I just left it in the form 2((x+2)^2 - (5/2)) and got confused.

Anyway, cheers, I really appreciate your help in all the topics that I post on this website, I really do. Hope Jesus will give you many women, you deserve them.
5. (Original post by frostyy)
Oh right, sorry. I just left it in the form 2((x+2)^2 - (5/2)) and got confused.

Anyway, cheers, I really appreciate your help in all the topics that I post on this website, I really do. Hope Jesus will give you many women, you deserve them.
Yay! Glad that cleared things up. Cheers, mate - don't worry about it.

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: April 7, 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

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

Chat with other maths applicants