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strange q in 2003 maths mock

  • 22-05-2007 2:54pm
    #1
    magher
    Registered Users, Registered Users 2 Posts: 202 ✭✭


    Does any one have any idea about Q5 B(ii) in the 2003 mock paper 1?
    I can't find an example in the book

    If log (a + b)/5 = 0.5(log a + log b)

    show that (a)(a) + (b)(b) = 23ab

    I was thinking of getting a in terms of b and subing into first formula?


Comments

  • #2
    seandoiler
    Registered Users, Registered Users 2 Posts: 107 ✭✭seandoiler


    magher wrote:
    Does any one have any idea about Q5 B(ii) in the 2003 mock paper 1?
    I can't find an example in the book

    If log (a + b)/5 = 0.5(log a + log b)

    show that (a)(a) + (b)(b) = 23ab

    I was thinking of getting a in terms of b and subing into first formula?

    well first off you've written the question wrong, which caused a bit of a problem!!

    If Log[ (a+b)/5 ] = 0.5 ( Log[a] + Log ), show a^2 + b^2 = 23 ab

    Soln: Log[ (a+b)/5 ] = 0.5 ( Log[a] + Log )
    Log[ (a+b)/5 ] = 0.5 ( Log[a b]) log of product equals sum of logs
    Log[ (a+b)/5 ] = Log[(ab)^0.5] number in front goes as power...def of log
    (a+b)/5 = (ab)^0.5 remove log
    (a^2+b^2+2ab)/25 = ab square both sides
    a^2+b^2 = 23 ab


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