You are Here: Home >< Maths

# The Binomial Expansion Help needed ASAP watch

1. Hi all, any help with the following question would be much appricated;

The first four terms, in ascending powers of x, of the binomial expansion of (1 +kx)n are

1+Ax+Bx2+Bx3+....

where k is a positive constant and A,B and n are psotitve integers

a) by considering the coefficients of x2 and x3, show that 3=(n-2)k

given that A=4

b) find the value of n and the value of k

Thanks in advance for any help
2. You start by expanding (1+kx)^n = 1 + nkx + (n(n-1)/2) (kx)^2 + (n(n-1)(n-2))/3!) (kx)^3 + ....

So B = n(n-1)k^2/2

and B also = n(n-1)(n-2)k^3/6

so (n-2)k/3 = 1

If A= 4 then nk = 4 and that gives you two equations in n and k to solve

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 31, 2010
Today on TSR

### Are you living on a tight budget at uni?

From budgets to cutbacks...

### University open days

1. University of Cambridge
Wed, 26 Sep '18
2. Norwich University of the Arts
Fri, 28 Sep '18
3. Edge Hill University
Faculty of Health and Social Care Undergraduate
Sat, 29 Sep '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