# Binomial Theorem (1 Viewer)

#### yeyjasminetime

##### Member

Hi guys,

I've been stuck on this binomial theory question (find the coefficient of x^3)

HHHNNNNGGGG what am I doing wrong?

Many thanks,
Frustrated girl

#### Drongoski

##### Well-Known Member
Term in x^3 can only come from term in x of part-1 factor multiplied by the term in x^2 in part-2 factor.This term in x^3 is given by:

(-5x) * 4C1 x^2 * (-3)^3

.: the coeff = (-5) x 4 x (-27) = 540

if I have not made a silly boo boo.

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#### AnimeX

##### Member
You cannot do it using that terms method because you're multiplying two brackets together.
I've attached my solution in the link below:
http://imgur.com/sRx5Itf

#### yeyjasminetime

##### Member
Cool thanks!

I think I understand

#### yeyjasminetime

##### Member
If you have 4C1 ..the isn't it supposed to be (x^2)^3x(-3)^1?

#### yeyjasminetime

##### Member
no....Drongoski, what's wrong with my method though?

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#### Trebla

##### Administrator
Administrator
View attachment 29167

Hi guys,

I've been stuck on this binomial theory question (find the coefficient of x^3)

HHHNNNNGGGG what am I doing wrong?

Many thanks,
Frustrated girl
You're not supposed to add the extra k to 8 - 2k because that is not an index on x. It is an index on a constant.