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# C2 Binomial Expanison help watch

1. Hi, i have got an awnser to the below question part a, but im not sure if its right and i need help with part b.

In the binomial expansion, in ascending powers of x, of (1+ax)n, where a and n are constants, the coeffiecnt of x is 15. The coefficient of x2 and x3 are equal.

a) Find the value of a nad the value of n

b)find the coefficient of x3

any help is much appriciated
2. (Original post by beccajonesy)
Hi, i have got an awnser to the below question part a, but im not sure if its right and i need help with part b.

In the binomial expansion, in ascending powers of x, of (1+ax)n, where a and n are constants, the coeffiecnt of x is 15. The coefficient of x2 and x3 are equal.

a) Find the value of a nad the value of n

b)find the coefficient of x3

any help is much appriciated
3. i got a=6 and n=2.5
4. (Original post by beccajonesy)
i got a=6 and n=2.5
Me too.

So then you can do part b): find the coefficient of by applying the binomial expansion, substituting in those values.

Remember that when is not an integer, the binomial coefficients are defined without using n! (because n has to be an integer to get a factorial of it):

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