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    1. Write as a single Logarithm, then simplfy your answer

    I have written the bases in the brackets, its obvious which ones they are.

    2log(10)20- (log(10)5+log(10)8)

    = log(10)400/ log(10) 40 = log(10) 40/log(10)4 = log(10)10/log(10)1

    But the answer at the back is: log (10) 10=1

    log(8)25 + log(8)10 - 3log(8)5 = log(8) 250/ log (8) 125

    The answer at the back of the book is: log(8)2=1/3


    Thank you very much!
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    2log(10)20- (log(10)5+log(10)8)

    = log(10)(400/40) = log(10) 10 = 1

    log(8)25 + log(8)10 - 3log(8)5 = log(8) (250/125) = log(8)2=1/3

    log(a) (b) + log(a)(c) = log(a)(bc)

    log(a) (b) - log(a)(c) = log(a)(b/c)

    Different to the rule

    log(a)(b)/log(a)(c) = log(c)(b)
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    (Original post by LondonBoy)
    1. Write as a single Logarithm, then simplfy your answer

    I have written the bases in the brackets, its obvious which ones they are.

    2log(10)20- (log(10)5+log(10)8)

    = log(10)400/ log(10) 40 = log(10) 40/log(10)4 = log(10)10/log(10)1

    But the answer at the back is: log (10) 10=1

    log(8)25 + log(8)10 - 3log(8)5 = log(8) 250/ log (8) 125

    The answer at the back of the book is: log(8)2=1/3


    Thank you very much!
    wrong! - when you subtract logs you have to divide
    log(10)(400/40) = log(10) 10 = 1

    phil
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    (Original post by LondonBoy)
    1. Write as a single Logarithm, then simplfy your answer

    I have written the bases in the brackets, its obvious which ones they are.

    2log(10)20- (log(10)5+log(10)8)

    = log(10)400/ log(10) 40 = log(10) 40/log(10)4 = log(10)10/log(10)1

    But the answer at the back is: log (10) 10=1

    log(8)25 + log(8)10 - 3log(8)5 = log(8) 250/ log (8) 125

    The answer at the back of the book is: log(8)2=1/3


    Thank you very much!
    2log(10)20 - (log(10)5+log(10)8)
    = log(10)20² - (log(10)[8x5])
    = log(10)400 - log(10)40
    = log(10)[400/40]
    = log(10)10 = 1

    log(8)25 + log(8)10 - 3log(8)5
    = log(8)(25x10) - 3log(8)5
    = log(8)250 - log(8)5³
    = log(8)[250/5³]
    = log(8)2
    => 8x = 2
    x = log2/log8 = log2/log2³ = log2/3log2 = 1/3
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    (Original post by Phil23)
    log(10)(400/40) = log(10) 10 = 1
    wrong! - when you subtract logs you have to divide

    phil
    i love your posts.
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    (Original post by chewwy)
    i love your posts.
    cheers - you understand the second qeustion? cant make mistakes like that, lol - its reckless maths

    pk
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    Im still so confused on how you get from log10 400/ log10 40 to the next part

    can someone please explain it

    thanks!
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    (Original post by LondonBoy)
    Im still so confused on how you get from log10 400/ log10 40 to the next part

    can someone please explain it

    thanks!
    That expression should never appear

    Look at the explanations above and the rules of logs used
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    Ohhh legend i get it thanks.
 
 
 
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