You are Here: Home >< Maths

# C4 Binomial Expansion question. HELP!! watch

1. Hi.
How do you do part b? I checked the answers and it stated that x=0.1 has to be used. Why is that?

Could someone provide me with a detailed explanation of how to obtain the answer.

2. Is It not 7100 = 8 - 9x then find x and substitute into the series
3. (Original post by Anfanny)
Is It not 7100 = 8 - 9x then find x and substitute into the series
No because that value of x is outside the interval of validity.
4. (Original post by Anfanny)
Is It not 7100 = 8 - 9x then find x and substitute into the series
Could you elaborate?
5. (Original post by greentron6)

Hi.
How do you do part b? I checked the answers and it stated that x=0.1 has to be used. Why is that?

Could someone provide me with a detailed explanation of how to obtain the answer.

Note that the cube root of 7100 = cube root of 1000 x cube root of 7.1.

You have to use a small value of x so that it is within the interval of validity. The expansion does not converge for large x.
6. (Original post by Mr M)
Note that the cube root of 7100 = cube root of 1000 x cube root of 7.1.

You have to use a small value of x so that it is within the interval of validity. The expansion does not converge for large x.
So why don't I multiply the answer of 1.922... by 1000 at the end?
7. (Original post by greentron6)
So why don't I multiply the answer of 1.922... by 1000 at the end?
You need to multiply by the CUBE ROOT of 1000.
8. (Original post by Mr M)
You need to multiply by the CUBE ROOT of 1000.
Oh. I understand now. Thanks for your help.

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: January 14, 2017
Today on TSR

### University open days

Wed, 21 Nov '18
• Buckinghamshire New University
Wed, 21 Nov '18
• Heriot-Watt University
Wed, 21 Nov '18
Poll
Useful resources

### 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