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# P3 binonmial expansion watch

1. given |x|<4
expand the following in ascending powers of x up to x^3
(a) (4-x)^0.5
(b) (sin 3x) (4-x)^0.5

I can do (a) and the answer is 2 - x/4 - (x^2)/64 - (x^3)/512
But I dont know how to expand sin 3x which does seem to appear in the Edexcel specification.

btw, will there be some questions on binomial expansion of rational functions?
2. i dont think you have to expand the sin3x bracket as there is no power above it, just multiply sin3x by the terms u get from part a
3. (Original post by keisiuho)
given |x|<4
expand the following in ascending powers of x up to x^3
(a) (4-x)^0.5
(b) (sin 3x) (4-x)^0.5

I can do (a) and the answer is 2 - x/4 - (x^2)/64 - (x^3)/512
But I dont know how to expand sin 3x which does seem to appear in the Edexcel specification.

btw, will there be some questions on binomial expansion of rational functions?

you just multiply sin 3x with the answer of a, so in this case
sin 3x (2 - x/4 - (x^2)/64 - (x^3)/512)

Im not sure though.
4. I also believe this.
But the answer to (b) is:
6x - (3/4)x^2 - (579/64)x^3
5. I wonder if there is an expansion for sin functions
6. (Original post by keisiuho)
I wonder if there is an expansion for sin functions
There is, but you don't learn it till P5 or P6.
7. (Original post by Nylex)
There is, but you don't learn it till P5 or P6.
Great!

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