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    Logs is the only thing on C2 i'm really struggling on. Haven't done them for a while and don't know how to go about answering the questions where different bases are used, and where just a number is involved. Here are two examples. I would really appreciate some help.

    1. Solve, giving your answer to 3 significant figures:
    log2X + log4X = 2

    2a). Given that 3 + 2log2X = log2Y, show that Y=8(x)squared.

    b). Hence, or otherwise, find the roots (alpha sign) and (beta sign) where (alpha) < (beta), of the equation:
    3 + 2log2X = log2(14x - 3).

    c). Show that log2(alpha) = -2

    d). Calculate log2(beta), giving your answer to 3 significant figures.


    Thank you for any help you can give.
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    Question 1:

    lgx/lg2 + lgx/lg4 = 2

    lg4lgx + lg2lgx = 2lg2lg4
    (lg4 + lg2)lgx = 2lg2lg4
    lgx = 2lg2lg4 / (lg4 + lg2) = ...
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    (Original post by JasonN)

    Logs is the only thing on C2 i'm really struggling on. Haven't done them for a while and don't know how to go about answering the questions where different bases are used, and where just a number is involved. Here are two examples. I would really appreciate some help.

    1. Solve, giving your answer to 3 significant figures:
    log2X + log4X = 2

    2a). Given that 3 + 2log2X = log2Y, show that Y=8(x)squared.

    b). Hence, or otherwise, find the roots (alpha sign) and (beta sign) where (alpha) < (beta), of the equation:
    3 + 2log2X = log2(14x - 3).

    c). Show that log2(alpha) = -2

    d). Calculate log2(beta), giving your answer to 3 significant figures.


    Thank you for any help you can give.
    2)a) 3 + 2log2X = log2Y
    => 3 + log2X2 = log2Y
    =>2^( 3 + log2X2) = 2^(log2Y)
    => 23.2log2X2 = y
    => y = 8x2
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    (Original post by e-unit)
    2)a) 3 + 2log2X = log2Y
    => 3 + log2X2 = log2Y
    =>2^( 3 + log2X2) = 2^(log2Y)
    => 23.2log2X2 = y
    => y = 8x2
    Thank you for your reply, but can you please explain for me how you got to 2^( 3 + log2X2) = 2^(log2Y) I don't understand.

    and how you got from that to the answer.
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    He just introduced the two, and made the existing terms the order of the value "2".

    Did that make sense?
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    (Original post by Knogle)
    He just introduced the two, and made the existing terms the order of the value "2".

    Did that make sense?
    I understand what you mean, i just don't understand why that was done.

    What rule is that?
    And why does 2^(log2Y) = y

    Sorry for my lack of understanding, just haven't been taught it for a while.
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    (Original post by JasonN)
    I understand what you mean, i just don't understand why that was done.

    What rule is that?
    And why does 2^(log2Y) = y

    Sorry for my lack of understanding, just haven't been taught it for a while.
    That isn't a rule per se, it's just something he introduced to solve the equation.

    And this is a general rule of thumb: xlogxa = a.
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    (Original post by Knogle)
    That isn't a rule per se, it's just something he introduced to solve the equation.

    And this is a general rule of thumb: xlogxa = a.
    Right.

    And the number 2 was introduced as the base in this question is 2?
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    Pretty much, yes.
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    You can save time by also remembering loga - logb = log(a/b).
    in Q1 and Q2 apply this.
    So Q2 would be 3= log2(y/x^2) hence 2^3= y/x^2
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    (Original post by Knogle)
    lgx/lg2 + lgx/lg4 = 2
    You meant lnx/ln2+lnx/ln4=2 right?
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    (Original post by Pravin)
    You meant lnx/ln2+lnx/ln4=2 right?
    They're both correct.

    Actually, you can take logs of any base you like.

    ln = base e and lg = base 10
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    Anyone had a go at parts b/c/d.

    Just had another go and really am struggling.
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    For b, solve the quadratic equation 8x^2-14x+3=0 The solutions represent alpha and beta where alpha smaller than beta. I'm sure you can do c and d after this, good luck.
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    (Original post by Pravin)
    You meant lnx/ln2+lnx/ln4=2 right?
    Both are correct. ln is just loge.
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    (Original post by Knogle)
    Question 1:
    I'm stuck on this question and the above method of working out makes no sense to me

    atm all i know is to do

    logX/log2 + logX/log4=2
    and then

    logX*log4 + log2*logX = 2

    But after that i am lost
 
 
 
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