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# C2 MAT Question Help {Binomial Expansion} watch

1. Attachment 590706590708

So the first one is a question and the second one is the answer for the question.

I can understand powers of a & b add up to make 8 but I'm unsure how they just ignored the 1 in the brackets and how they got 2k in the equation.

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2. (Original post by Denisi007)

So the first one is a question and the second one is the answer for the question.

I can understand powers of a & b add up to make 8 but I'm unsure how they just ignored the 1 in the brackets and how they got 2k in the equation.

They've not ignored the 1 in the bracket. If we add some brackets, you can see that they are taking the binomial expansion of:

That is in the standard binomial expansion.

Terms in that expansion will be

Now, each term in the brackets has a sum of powers of 2.

xy: x=1,y=1, total=2
y^2:x=0,y=2, total =2

And when you raise what's in the brackets to the power of k, the power of any terms in the result will be 2k.

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