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    in the expansion of (1+x/2)^n in ascending powers of x the coefficient of x^2 is 30.
    a) find n
    b) find the first four terms of the expansion
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    (Original post by ramshahk)
    in the expansion of (1+x/2)^n in ascending powers of x the coefficient of x^2 is 30.
    a) find n
    b) find the first four terms of the expansion
    What is the coefficient of x^2 in terms of n in the expansion?
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    (Original post by SeanFM)
    What is the coefficient of x^2 in terms of n in the expansion?
    30
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    (Original post by ramshahk)
    30
    As I specified in my post - in terms of n?

    Or, what are the first 3 terms in the expansion of (1+(x/2))^n?
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    (Original post by ramshahk)
    in the expansion of (1+x/2)^n in ascending powers of x the coefficient of x^2 is 30.
    a) find n
    b) find the first four terms of the expansion
    Can I encourage you to post A level maths questions in F38 (the Maths Forum)?

    Could you use the formula in your formula book to write down the x^2 term in the expansion?
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    (Original post by Mr M)
    Can I encourage you to post A level maths questions in F38 (the Maths Forum)?

    Could you use the formula in your formula book to write down the x^2 term in the expansion?
    i have tried but it doesnt work
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    (Original post by ramshahk)
    i have tried but it doesnt work
    Really? Can you post your working? A photo will do (assuming it is the right way up).
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    (Original post by Mr M)
    Really? Can you post your working? A photo will do (assuming it is the right way up).
    sorry i threw the working out in the bin ahaha
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    (Original post by ramshahk)
    sorry i threw the working out in the bin ahaha
    i dont know how to use the formula with this question
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    (Original post by ramshahk)
    i dont know how to use the formula with this question
    Ok I'll start you off.

    (1+\frac{x}{2})^n = 1 + n(\frac{x}{2})+\frac{n(n-1)}{2!}(\frac{x}{2})^2 +...

    You'll need to do some simplification and add a fourth term.
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    (Original post by Mr M)
    Ok I'll start you off.

    (1+\frac{x}{2})^n = 1 + n(\frac{x}{2})+\frac{n(n-1)}{2!}(\frac{x}{2})^2 +...

    You'll need to do some simplification and add a fourth term.
    yeah what do you do after that
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    (Original post by ramshahk)
    yeah what do you do after that
    Use the fact that the coefficient of x^2=30. You'll need to form and solve a quadratic to find the value of n.
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    (Original post by Mr M)
    Use the fact that the coefficient of x^2=30. You'll need to form and solve a quadratic to find the value of n.
    ??
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    (Original post by ramshahk)
    ??
    I'm getting the impression this is too difficult for you at the moment. Could you ask your teacher to explain it to you tomorrow?
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    (Original post by Mr M)
    I'm getting the impression this is too difficult for you at the moment. Could you ask your teacher to explain it to you tomorrow?
    haha okay will do
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    ramshahk Mr M has told you how to find the coefficient of x^2 algebraically (in terms of n).
    You know that this is equal to 30 so can you form an equation with these two pieces of information in order to solve n?
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    (Original post by surina16)
    @ramshahk Mr M has told you how to find the coefficient of x^2 algebraically (in terms of n).
    You know that this is equal to 30 so can you form an equation with these two pieces of information in order to solve n?
    yeah i get that bit
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    (Original post by ramshahk)
    yeah i get that bit
    Great, so what did you get for n?
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    (Original post by surina16)
    Great, so what did you get for n?
    i didnt find out n
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    (Original post by ramshahk)
    i didnt find out n
    Mr M has given you the first few terms of the expansion. See that term with 3rd term (\frac{x}{2})^2?? Rewrite it as A \cdot x^2 where A is a function of n and make it equal to 30. Then solve for n.
 
 
 
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