I understand Binomial Theorem, but this was an extension question and I can't find the answer. 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.
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$\displaystyle (a+b)^n=\sum\limits_{k=0}^n {n \choose k}a^{n-k}b^k$. So the first three terms are: $\displaystyle {n\choose 0}a^nb^0 +{n \choose 1}a^{n-1}b^1+{n \choose 2}a^{n-2}b^2$. Take it from there...
Write out the first three terms of the expansion and compare it to 1-3x+15x^2/4.
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