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# Finding value independent of x in a binomial expansion?

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1. A = 420
k = 2

These were worked out from the earlier part (a)

What is the method of calculating the independent term ? Someone plz help

Thanks
2. Find for r=5 (this I did by recognition and some thought...dont really think there is a 'method')

edit: So
Spoiler:
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15C5 k^5 = 3003*32= 96096 I think...

3. I agree with the above post too, just find an r value so that the terms cancel.
4. what is the r?

5. that is, the fomrula for a binomial expansion, putting n=15

So the general term is

Can you find a value of r such that the power of x is zero? (Get the x indices together and solve the equation, or just do it by inspection). Evaluate the general term for this value of r.
6. nCr. Number of ways of choosing r objects from n items.

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