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# (a+b)^n and (1+x)^n..whats the difference? watch

1. (a+b)^n and (1+x)^n..whats the difference?
2. (Original post by ShOcKzZ)
(a+b)^n and (1+x)^n..whats the difference?
The binomial expansion only works for (1+x)^n so you have to take out a factor of a^n from the first if you're going to use the normal expansion
(a+b)^n = a^n(1+b/a)^n
3. (Original post by Bezza)
The binomial expansion only works for (1+x)^n so you have to take out a factor of a^n from the first if you're going to use the normal expansion
(a+b)^n = a^n(1+b/a)^n
You can still use the nCr thing for (a + b)^n though.

(a + b)^n = a^n + (nC1)a^(n - 1)b^1 + (nC2)a^(n - 2)b^2 + ... + b^n
4. (Original post by Nylex)
You can still use the nCr thing for (a + b)^n, yeah?

(a + b)^n = a^n + (nC1)a^(n - 1)b^1 + (nC2)a^(n - 2)b^2 + ... + b^n
Yeah, but in the a-level formula book they give you the expansion for (1+x)^n so it's easiest just to rearrange and use it (in my opinion)
5. (Original post by Bezza)
The binomial expansion only works for (1+x)^n so you have to take out a factor of a^n from the first if you're going to use the normal expansion
(a+b)^n = a^n(1+b/a)^n
i c

so would (2 + 3x)^5 = 2^5.(1 + 1.5x)^5 ?
6. (Original post by ShOcKzZ)
i c

so would (2 + 3x)^5 = 2^5.(1 + 1.5x)^5 ?
Yep
7. (Original post by Bezza)
Yep
thanks.

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