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Math Help - imaginary numbers

  1. #1
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    imaginary numbers

    (4 + 5i)^2 - (4 - 5i)^2
    I have to write it in standard form a + bi
    I am having trouble with this problem...I got an answer, but it is incorrect...could someone please help me?
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  2. #2
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    Quote Originally Posted by aikenfan View Post
    (4 + 5i)^2 - (4 - 5i)^2
    I have to write it in standard form a + bi
    I am having trouble with this problem...I got an answer, but it is incorrect...could someone please help me?
    Difference of two squares,
    (4+5i + 4 - 5i)(4+5i - 4 + 5i) = 8*10i = 0 + 80i
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  3. #3
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    If z = x + yi then
    z^2  - \overline z ^2  = \left( {z + \overline z } \right)\left( {z - \overline z } \right) = \left( {2x} \right)\left( {2yi} \right)<br />
.
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  4. #4
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    Quote Originally Posted by aikenfan View Post
    (4 + 5i)^2 - (4 - 5i)^2
    I have to write it in standard form a + bi
    I am having trouble with this problem...I got an answer, but it is incorrect...could someone please help me?
    Foil it out:
    (4 + 5i)^2 - (4 - 5i)^2

    = (16 + 40i + 25i^2) - (16 - 40i + 25i^2)

     = 80i

    -Dan
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  5. #5
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    Quote Originally Posted by ThePerfectHacker View Post
    Difference of two squares,
    (4+5i + 4 - 5i)(4+5i - 4 + 5i) = 8*5i = 0 + 40i
    You sure?
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  6. #6
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    Quote Originally Posted by Krizalid View Post
    You sure?
    Thank you I fixed it. I had too much to drink.
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  7. #7
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    Thank you all very much! I've been working at that problem for the longest time but i just couldnt get it, but now i know what i was doing wrong! I forgot that it was squared when i copied it onto my paper
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