# Binomial Theorem

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• May 4th 2012, 12:20 PM
mcshine
Binomial Theorem
I understand Binomial Theorem, but this was an extension question and I can't find the answer.

Quote:

In the expansion of (1+bx)^n , the first three terms are 1-3x+(15/4)x^2. Find b and n.

Could someone please help me? Thanks.
• May 4th 2012, 12:29 PM
MathoMan
Re: Binomial Theorem
$(a+b)^n=\sum\limits_{k=0}^n {n \choose k}a^{n-k}b^k$.

So the first three terms are: ${n\choose 0}a^nb^0 +{n \choose 1}a^{n-1}b^1+{n \choose 2}a^{n-2}b^2$.

Take it from there...
• May 4th 2012, 12:30 PM
a tutor
Re: Binomial Theorem
Write out the first three terms of the expansion and compare it to 1-3x+15x^2/4.