Year 12s: what will be the first way you research your future options? >>

C4 - Binomial Expansion

Need help with 5ii. I don't fully understand what exactly I have to do. Can someone explain it to me. Thanks.

http://www.ocr.org.uk/Images/62967-question-paper-4724-core-mathematics-4.pdf

Plug the value in

Original post by seizetoday

Plug the value in

Right I get 37/49 when I do that. I don't get the first bit of the mark scheme where do they get that from. The root of 5 over 3?
http://www.ocr.org.uk/Images/62961-mark-scheme-june.pdf

Reply 3

davros

Original post by Super199

Right I get 37/49 when I do that. I don't get the first bit of the mark scheme where do they get that from. The root of 5 over 3?
http://www.ocr.org.uk/Images/62961-mark-scheme-june.pdf

Where on earth do you get 37/49 from?

If x = 2/7 then what is 1 - x? What is 1 + x? So what is (1 - x) / (1 + x)?

Reply 4

Super199

Original post by davros

Where on earth do you get 37/49 from?

If x = 2/7 then what is 1 - x? What is 1 + x? So what is (1 - x) / (1 + x)?

37/49 is what you get if you put 2/7 into that expansion.

You get 5/9 for what you asked. Which square rooted gives root5/3.

Reply 5

TenOfThem

Original post by Super199

37/49 is what you get if you put 2/7 into that expansion.

You get 5/9 for what you asked. Which square rooted gives root5/3.

So ... You are ok now?

Reply 6

davros

Original post by Super199

37/49 is what you get if you put 2/7 into that expansion.

You get 5/9 for what you asked. Which square rooted gives root5/3.

So now you can put the 2 pieces together to get the answer they ask for :smile:

Reply 7

Super199

Original post by TenOfThem

So ... You are ok now?

Original post by davros

So now you can put the 2 pieces together to get the answer they ask for :smile:

Yeah I got it but I wouldn't have thought of doing that.

Reply 8

TenOfThem

Original post by Super199

Yeah I got it but I wouldn't have thought of doing that.

This is a fairly standard application of binomial expansion

Reply 9

davros

Original post by Super199

Yeah I got it but I wouldn't have thought of doing that.

This type of question seems to come up quite regularly, although most of the ones I have seen actually ask for a decimal approximation rather than just a fraction as the output.