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Math Help - Quotient Rule Question

  1. #1
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    Quotient Rule Question

    Hi, i'm using an online evaluation tool, and it's not excepting my answer. There are 2 reasons for this.

    1) My answer input is wrong
    2) The machine is wrong

    Now i've done the question 3 or 4 times now with differing answers only in + & - signs, but input all answers into the tool and it always comes back as wrong.

    This is the question

    differentiate \frac{3x+2}{7x^2+9x+8}

    i'm using the quotient rule as i know it which is

    \frac{(v.u')-(u.v')}{v^2}

    and i get this as my answer

    \frac{-21x^2-28x+6}{49x^4+126x^3+193x^2+144x+64}


    So am i right, or am i wrong?
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  2. #2
    Banned
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    your answer is correct, but the machine might only be accepting one exact answer.. i'd try factoring a -1 from the numerator, but other than that I'm not sure
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  3. #3
    Junior Member
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    ok, so i got the solutions and aparently this is the solution...

    \frac{-20(21x^2+28x-6)}{(7x^2+9x+8)^2}

    so i am completely stumped! I'm hoping maths hasn't been broken and the lecturer has just got tired and put -20 instead of -1.
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  4. #4
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    yeah that's wrong, if you take the antiderivative of that you get an extra factor of 20, which we do not want

    that 20 shouldnt be there if you've stated the problem correctly
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