You are Here: Home >< Maths

binomial help Watch

1. hey

I have came across an unfamiliar binomial question which I am unsure of

"Find the term independent of x in the binomial expansion of

(3x + 1/x2)9"

How would I do this? Thanks
2. (Original post by upthegunners)
hey

I have came across an unfamiliar binomial question which I am unsure of

"Find the term independent of x in the binomial expansion of

(3x + 1/x2)9"

How would I do this? Thanks
The eaxpansion means szum of 10 terms (from k=0 ..9)
that is

for k th term

This independent from x when 9-k=2k -> k=3
The 4th term.
the value of it
3. The first term will be

(number) (3x)^9

The next term will be

(number) (3x)^8 (1/x^2)^1 = (number) (x^6)

Continue this until you find the one with just a number

Then work out the coefficient
4. (Original post by TenOfThem)
The first term will be

(number) (3x)^9

The next term will be

(number) (3x)^8 (1/x^2)^1 = (number) (x^6)

Continue this until you find the one with just a number

Then work out the coefficient
Is there not a quicker method?
5. (Original post by upthegunners)
Is there not a quicker method?
Realising that there is an obvious pattern and that you need

(number) (3x)^a (1/x^2)^b

where a+b = 9

and a-2b = 0

ie post 2

however, I went for a simpler approach based on my understanding of your capabilities

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: April 12, 2013
Today on TSR

What is the latest you've left an assignment

And actually passed?

Simply having a wonderful Christmas time...

Discussions on TSR

• Latest
• See more of what you like on The Student Room

You can personalise what you see on TSR. Tell us a little about yourself to get started.

• 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

Chat with other maths applicants

Groups associated with this forum:

View associated groups
Discussions on TSR

• Latest
• See more of what you like on The Student Room

You can personalise what you see on TSR. Tell us a little about yourself to get started.

• 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.