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Math Help - For exam tomorrow. Complex numbers.

  1. #1
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    For exam tomorrow. Complex numbers.

    Arg, this mark scheme is...rubbish...

    Okey, use the fact the suare root of 16 + 30i is (-5 - 3i) and (5 + 3i)

    To work out z^2 - 2z - (15 + 30i)

    Using the formula i got to this stage and got stuck =(

    2 + or - \frac{\sqrt{64 + 120i}}{2}

    Now i notice if you \ the fraction by 4 you get 16 + 30i which your meant to use...but you can't just do that so uh..wt..

    Any help, i'd appreciate loads! Thanks (answer is 6 + 3i and -4 - 3i)

    tytyty
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    Moo
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    Hi !

    Quote Originally Posted by AshleyT View Post
    Arg, this mark scheme is...rubbish...

    Okey, use the fact the suare root of 16 + 30i is (-5 - 3i) and (5 + 3i)

    To work out z^2 - 2z - (15 + 30i)

    Using the formula i got to this stage and got stuck =(

    2 + or - \frac{\sqrt{64 + 120i}}{2}

    Now i notice if you \ the fraction by 4 you get 16 + 30i which your meant to use...but you can't just do that so uh..wt..

    Any help, i'd appreciate loads! Thanks (answer is 6 + 3i and -4 - 3i)

    tytyty
    It's nice that you noticed that

    \sqrt{64+120i}=\sqrt{4(16+30i)}=2 \sqrt{16+30i}

    I think that's all you need here

    Just show your work if you have further difficulties, it'll be rather better to help you understand
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  3. #3
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    Quote Originally Posted by Moo View Post
    Hi !



    It's nice that you noticed that

    \sqrt{64+120i}=\sqrt{4(16+30i)}=2 \sqrt{16+30i}

    I think that's all you need here

    Just show your work if you have further difficulties, it'll be rather better to help you understand
    O yea! Can't believe missed that...

    Thank-you very much!!
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