Results 1 to 7 of 7

Math Help - What the?

  1. #1
    Newbie
    Joined
    Jan 2006
    Posts
    7

    What the?

    Can anyone help me with these..?!


    1) 3i/2+5i

    and...

    2) square root of -2(square root of -9 - square root of 7)

    i would appreicate it if you can reply asap.

    P.S: only reply if u KNOW the answer...thanks.
    Last edited by ThePerfectHacker; January 22nd 2006 at 02:06 PM.
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Grand Panjandrum
    Joined
    Nov 2005
    From
    someplace
    Posts
    14,972
    Thanks
    4
    Quote Originally Posted by MOODYtarqi
    Can anyone help me with these..?!


    1) 3i/2+5i
    This is ambiguous (you need to use brackets to make this unambiguous),
    but I will presume you are asking for:

    \frac{3i}{2+5i}

    to be reduced to standard form a+b.i.

    Multiply the top and bottom by the complex conjugate of the bottom:

    \frac{3i}{2+5i} = \frac{3i (2-5i)}{(2+5i)(2-5i)},

    so:

    \frac{3i}{2+5i} = \frac{15+6i}{29}=\frac{15}{29}+\frac{6i}{29}.

    RonL
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Newbie
    Joined
    Jan 2006
    Posts
    7
    thanks man you're smart . . . or I'm an idiot.

    appreciate it.
    Follow Math Help Forum on Facebook and Google+

  4. #4
    Grand Panjandrum
    Joined
    Nov 2005
    From
    someplace
    Posts
    14,972
    Thanks
    4
    Quote Originally Posted by MOODYtarqi

    2) square root of -2(square root of -9 - square root of 7)
    This again is ambiguous, it could mean either:

    \sqrt{-2(\sqrt{-9}-\sqrt{7}}),

    or:

    \sqrt{-2}(\sqrt{-9}-\sqrt{7}).

    I will assume that you mean the latter of these, then:

    \sqrt{-2}(\sqrt{-9}-\sqrt{7})=\sqrt{2}i(3i-\sqrt{7})

    so:

    \sqrt{-2}(\sqrt{-9}-\sqrt{7})=-3\sqrt{2}-\sqrt{14}i

    RonL
    Follow Math Help Forum on Facebook and Google+

  5. #5
    Newbie
    Joined
    Jan 2006
    Posts
    7
    thanks again. but what if the tell me "write it in standard form?"
    Follow Math Help Forum on Facebook and Google+

  6. #6
    Grand Panjandrum
    Joined
    Nov 2005
    From
    someplace
    Posts
    14,972
    Thanks
    4
    Quote Originally Posted by MOODYtarqi
    thanks again. but what if the tell me "write it in standard form?"
    They have both been reduced to standard form (or near enough to get marked as correct).

    RonL
    Follow Math Help Forum on Facebook and Google+

  7. #7
    Newbie
    Joined
    Jan 2006
    Posts
    7
    thanks man... have a Gday.
    Follow Math Help Forum on Facebook and Google+


/mathhelpforum @mathhelpforum