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# Using binomial expansion to find bx watch

1. I got this far:

and I'm completely lost. I'm pretty sure the questions in this book are much more advanced than the ones I will most likely be asked in an exam, but still, it frustrates me that I'm unable of completing it.
2. (Original post by frostyy)
and I'm completely lost. I'm pretty sure the questions in this book are much more advanced than the ones I will most likely be asked in an exam, but still, it frustrates me that I'm unable of completing it.
It's not (3 choose 1)(bx), it's (n choose 1)(bx).

So your expansion should start as 1 + bnx + ...

Then bn = 28, and the coefficient of x^2 = 336 gives simultanous equations in b and n which you can solve.

The book has given the first three terms, not that there are three terms in total.
3. n does not have to be 3. Try expanding (1+bx)^n generally
4. that's just ****ing stupid
im dropping out
5. (Original post by frostyy)
that's just ****ing stupid
im dropping out
Happens to all of us!

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