Expansions in C2

For expansions in C2 can you use the the C4 method? or does it depend?

Yes you can use either of the binomial expansion results, though questions are usually designed so you don't need to.


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Thank you!

The expansion used in A2 can be especially useful in AS if you are solving for an unknown value of the power of the binomial.


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Sorry what do you mean by this?

7. The first four terms, in ascending powers of x, of the binomial expansion of (1 + kx)^n are

1 + Ax + Bx^2 + Bx^3 + …, where k is a positive constant and A, B and n are positive integers.

(a) By considering the coefficients of x^2 and x^3, show that 3 = (n – 2) k.
(4)
Given that A = 4, (b) find the value of n and the value of k.
(4)

from the original C2 mock paper

As you don't know n, you can't just hit the nCr button

I see, makes sense. But in pretty much everything else is it okay to use the c4 expansion method?

7. The first four terms, in ascending powers of x, of the binomial expansion of (1 + kx)^n are

1 + Ax + Bx^2 + Bx^3 + …, where k is a positive constant and A, B and n are positive integers.

(a) By considering the coefficients of x^2 and x^3, show that 3 = (n – 2) k.
(4)
Given that A = 4, (b) find the value of n and the value of k.
(4)

from the original C2 mock paper

As you don't know n, you can't just hit the nCr button

How come they've put this in a C2 mock? Surely the A2 method isn't known to AS students?

How come they've put this in a C2 mock? Surely the A2 method isn't known to AS students?