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    (Original post by Geraer100)
    June 2000, step ii, q3,

    When a, b and c are small, why (1+(13a-2b+24c)/49)^1/2 is more or less equal to (1+(13a-2b+24c)/98)), with just the denominator doubled?
    sqrt(1+a) approx 1 + a/2 by the binomial expansion
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    I also did STEP II 2015 today

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    Q1) I liked this question.
    Q4) Lovely, though I spent too long on it really.
    Q5) Nice question, but it took longer than I would have liked.
    Q6) Alright. The first two parts were straightforward. Made a silly algebra mistake in the final part.
    Q7) I am annoyed at this. I had an expression for y, but thought it was too ugly to be correct so crossed it out and tried to start again. Turns out I was actually right in the first place.

    Overall: I got a solid 1 so I am happy, though I would have preferred to atleast start a 6th question.

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    STEP II 2015:
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    Seems like I missed out on not attempting 4 or 5. I'm a bit surprised no-one else tried 3, it turned out to be pretty easy IMO.

    Edit: Definitely missed out on with 4, would've been an easy 15 marks certainly.
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    (Original post by Zacken)
    sqrt(1+a) approx 1 + a/2 by the binomial expansion
    Okay, many thanks!
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    (Original post by Vesniep)
    I've done the paper today.
    Well done!

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    Did you do the first part in the same way as the mark scheme? I tried doing it by saying C = ky + 0P(X<=y) + a(X-y)P(X > y) = ky + a(X-y)(1 - (1 - e^(-lambday))) and then doing E(C) as E(ky - aye^(-lambday)) + ae^-(lambday)E(X), but that didn't get me the right answer as I had an extra aye^(-lambday) term.
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    (Original post by EnglishMuon)
    Just a quick check: when showing arcoshx= ln{1+(x^2-1)^1/2} I am able to look at cosh { ln{1+(x^2-1)^1/2}}= x and deduce the result from this?
    And mention ln(x + root(x^2 - 1)) is positive so that it is arcosh x and not -arcosh x?
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    (Original post by 16Characters....)
    And mention ln(x + root(x^2 - 1)) is positive so that it is arcosh x and not -arcosh x?
    and yep, did put that in my workings
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    (Original post by sweeneyrod)
    Well done!

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    Did you do the first part in the same way as the mark scheme? I tried doing it by saying C = ky + 0P(X<=y) + a(X-y)P(X > y) = ky + a(X-y)(1 - (1 - e^(-lambday))) and then doing E(C) as E(ky - aye^(-lambday)) + ae^-(lambday)E(X), but that didn't get me the right answer as I had an extra aye^(-lambday) term.
    E(C) = P(X<y) * E(ky) + P(X>y) * E(ky+a(X-y) I Y>y ) =ky+ a e^(-λy) (E(X I X>y) - y)
    E( X I X>y)= [ integral of (λe^(-λχ)) from y to infinity ] / P(X>y) = y + 1/λ
    Comment : I know it was quiet difficult and it got me into trouble .
    part ii was too much , very messy integrals I don't see the point
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    just did 2013 ii - 105
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    (Original post by Vesniep)
    E(C) = P(X<y) * E(ky) + P(X>y) * E(ky+a(X-y) I Y>y ) =ky+ a e^(-λy) (E(X I X>y) - y)
    E( X I X>y)= [ integral of (λe^(-λχ)) from y to infinity ] / P(X>y) = y + 1/λ
    Comment : I know it was quiet difficult and it got me into trouble .
    part ii was too much , very messy integrals I don't see the point
    I see, I forgot the given part. Thanks
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    When explaining a simple idea such as the first part of q5 III 2001, is it usually acceptable to use a diagram instead of words? i.e. in this case is it enough to differentiate and show f(x) is an increasing function and then give a rough sketch of a strictly increasing cubic (instead of saying as x tends to +- infinity....)? (followed by stating the conclusion)
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    (Original post by 16Characters....)
    I also did STEP II 2015 today
    Spoiler:
    Show

    Q1) I liked this question.
    Q4) Lovely, though I spent too long on it really.
    Q5) Nice question, but it took longer than I would have liked.
    Q6) Alright. The first two parts were straightforward. Made a silly algebra mistake in the final part.
    Q7) I am annoyed at this. I had an expression for y, but thought it was too ugly to be correct so crossed it out and tried to start again. Turns out I was actually right in the first place.

    Overall: I got a solid 1 so I am happy, though I would have preferred to atleast start a 6th question.

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    Q3 was very easy btw .
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    (Original post by Number Nine)
    just did 2013 ii - 105
    which q's
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    (Original post by Vesniep)
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    Q3 was very easy btw .
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    Not as easy as q2, one of the easiest questions for m ever,
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    (Original post by EnglishMuon)
    When explaining a simple idea such as the first part of q5 III 2001, is it usually acceptable to use a diagram instead of words? i.e. in this case is it enough to differentiate and show f(x) is an increasing function and then give a rough sketch of a strictly increasing cubic (instead of saying as x tends to +- infinity....)? (followed by stating the conclusion)
    It would be more rigorous especially if you mention Bolzano's theorem for continuous functions (at least one root) and that it's a 1-1 function (at most 1 root) but perhaps they'd accept it
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    (Original post by physicsmaths)
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    Not as easy as q2, one of the easiest questions for m ever,
    Didn't try it yet . I thought geometry => let's move on
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    (Original post by gasfxekl)
    which q's
    1,2,3,5,7,8
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    (Original post by Vesniep)
    It would be more rigorous especially if you mention Bolzano's theorem for continuous functions (at least one root) and that it's a 1-1 function (at most 1 root) but perhaps they'd accept it
    I mean i cant imagine mentioning bolzanos theorem would get u any more credit especially as you are not required to know it and it is just the same as saying there is only 1 root if u dont give proof.
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    (Original post by EnglishMuon)
    Just a quick check: when showing arcoshx= ln{1+(x^2-1)^1/2} I am able to look at cosh { ln{1+(x^2-1)^1/2}}= x and deduce the result from this?
    Well yes.


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    (Original post by EnglishMuon)
    When explaining a simple idea such as the first part of q5 III 2001, is it usually acceptable to use a diagram instead of words? i.e. in this case is it enough to differentiate and show f(x) is an increasing function and then give a rough sketch of a strictly increasing cubic (instead of saying as x tends to +- infinity....)? (followed by stating the conclusion)
    Yep that is perfectly fine. Infact much better.


    Posted from TSR Mobile
 
 
 
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