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    Hi, Just need some help


    Part C of the question indicates f(t)=ke^t, and that means 3-2e^-x = ke^t. Could someone explain why?
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    It doesn't? It doesn't say they are equal to each other anywhere as far as I can tell

    Or are you looking at the mark scheme?
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    (Original post by Fanatical Geek)
    It doesn't? It doesn't say they are equal to each other anywhere as far as I can tell

    Or are you looking at the mark scheme?
    Had no clue what to do with the question so I looked it up

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    (Original post by suibster)
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    Hi, Just need some help


    Part C of the question indicates f(t)=ke^t, and that means 3-2e^-x = ke^t. Could someone explain why?
    In this situation x=t so f(x) = 3-2e^-x can be written as f(t) = 3-2e^-t

    As such you can write f(t) = ke^t as 3-2e^-t = ke^t

    I think...
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    (Original post by Narxs)
    In this situation x=t so f(x) = 3-2e^-x can be written as f(t) = 3-2e^-t

    As such you can write f(t) = ke^t as 3-2e^-t = ke^t

    I think...
    Thanks.. The answer makes sense but I don't understand why you would make x=t at the first place.
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    (Original post by suibster)
    Thanks.. The answer makes sense but I don't understand why you would make x=t at the first place.
    The function f is constant for this question as it has not been redefined, (i.e. saying f: y -> y^3 +3) the only thing changing is the variable you sub into it.
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    (Original post by Narxs)
    The function f is constant for this question as it has not been redefined, (i.e. saying f: y -> y^3 +3) the only thing changing is the variable you sub into it.
    I see, so you're saying that you've just decided to make f(x) = f(t) and just sub it in for no reason?
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    if it says f(t) that means you change the x to t, same as if it were to say f(2) you would sub 2 into the x.

    After that you just times all by e^t (since you can just write the 2e^-t as 2/e^t) to make it into a positive which then gives you a quadratic equation.

    from there its just straight forward
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    (Original post by suibster)
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    Hi, Just need some help


    Part C of the question indicates f(t)=ke^t, and that means 3-2e^-x = ke^t. Could someone explain why?
    What paper is this?
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    (Original post by BusinessLover18)
    What paper is this?
    JAN 2014 IAL C3 edexcel
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    thank you!
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    Multiply each term by e^t which will then give you a quadratic.
    Because it only has 1 real solution set the discriminant (b^2 - 4ac) equal to 0 and find k. Hope this helps! (:
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    (Original post by suibster)
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    Hi, Just need some help


    Part C of the question indicates f(t)=ke^t, and that means 3-2e^-x = ke^t. Could someone explain why?
    what paper is this from? Just curious.
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    (Original post by suibster)
    JAN 2014 IAL C3 edexcel
    (Original post by XxKingSniprxX)
    what paper is this from? Just curious.
    ...
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    (Original post by blahblah21)
    Multiply each term by e^t which will then give you a quadratic.
    Because it only has 1 real solution set the discriminant (b^2 - 4ac) equal to 0 and find k. Hope this helps! (:

    thank you! My question is how do you know that you'd make f(t) = f(x) and not just to work out the question f(t)= ke^t on its own?
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    (Original post by suibster)
    thank you! My question is how do you know that you'd make f(t) = f(x) and not just to work out the question f(t)= ke^t on its own?
    Oh, it's like saying f(3) you would sub in 3 for x. Same principle applies sub in t for x. Hope this kinda helps (:
 
 
 
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