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    Can someone help in part C?
    I got that the modulus of X should be less than 1 but mark scheme states that it must be less than half. Can anyone explain why?


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    (Original post by Lilly1234567890)
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    Can someone help in part C?
    I got that the modulus of X should be less than 1 but mark scheme states that it must be less than half. Can anyone explain why?


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    |2x| < 1
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    (Original post by Lilly1234567890)
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    Can someone help in part C?
    I got that the modulus of X should be less than 1 but mark scheme states that it must be less than half. Can anyone explain why?


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    because of the  \displaystyle \left(1+2x\right) term on the bottom of the fraction

    I havent done the question so i dont know what the partial fractions are but at some stage you have to expand  \displaystyle \left(1+2x\right)^{-1} using the binomial expansion, this is why |x|<0.5
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    (Original post by Lilly1234567890)
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    Can someone help in part C?
    I got that the modulus of X should be less than 1 but mark scheme states that it must be less than half. Can anyone explain why?


    Posted from TSR Mobile
    In general, the expansion of (1+ax)^{n} for non-natural n is only valid for |ax| &lt; 1.
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    (Original post by Zacken)
    In general, the expansion of (1+ax)^{n} for non-natural n is only valid for |ax| &lt; 1.
    what if we look at the other expansion 1-x, wont it then be the modulus of x is less than 1
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    (Original post by Lilly1234567890)
    what if we look at the other expansion 1-x, wont it then be the modulus of x is less than 1
    Yes.
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    (Original post by Lilly1234567890)
    what if we look at the other expansion 1-x, wont it then be the modulus of x is less than 1
    But you are doing two expansions. You need the range of values for which both are valid, i.e. the smaller range.
 
 
 
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