A level Maths Binomials help

The question is - in the expansion of (1+kx)^n the coefficients of x and x^2 are 12 and 60 respectively. Find k and n.

I expanded this and got (nC1)kx +(nc2)k^2x^2
so nk=12 and nc2k^2=60

How do I solve it?

Reply 1

Ria214

Did you use the formula from the forumla booklet?

Reply 2

epic08

Original post by Ria214

Did you use the formula from the forumla booklet

so nc2 wold equal = n!/2!(n-2)! ?

but then I still don't get how that helps me solve it?

(edited 2 years ago)

Reply 3

davros

Original post by epic08

so nc2 wold equal = n!/2!(n-2)! ?

but then I still don't get how that helps me solve it?

It would be more helpful to use the form n(n-1)/2 for the coefficient of the x^2 term if you've seen this before. If you haven't, note that your binomial coefficient simplifies enormously - 2! is just 2 x 1 = 2, and n! = n(n-1)(n-2)! by definition, so you can do some cancelling :smile: