Binomial Thoerem question (1 Viewer)

[NizDiz]

Find the co-efficient of:

x in (1 + 2x + 3x^2) (1 - 2/x)^5

 

[Drongoski]

I think it is:

 

[NizDiz]

how'd u do it that easily?

 

[Drongoski]

When you multiply the first factor(a trinomial) with the binomial expansion, you can obtain terms in x only from the product of the 2nd term of the trinomial with the 1st (the constant term) of the expansion and the product of the 3rd term of the trinomial with the 2nd term of the expansion, which added together gives you (2-30)x


"how'd u do it so easily?": - if you have as many years of practice as I have, you'd be able to do it just as easily.

 

[levaly]

Answer is 28.

You can check out this step by step expansion: http://www.symbolab.com/solutions/e...x+3x^{2}\right)\left(1-\frac{2}{x}\right)^{5}

 

[braintic]

Answer is 28.

You can check out this step by step expansion: http://www.symbolab.com/solutions/e...x+3x^{2}\right)\left(1-\frac{2}{x}\right)^{5}

No, your link confirms the answer is -28, not 28.
Also, the point of this question is to understand how to find the x term directly without writing out the whole expansion. So your link is not particularly useful.
It seems from your 8 posts so far that your account was set up solely to promote this website.