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Math Help - Write your answer in a + bi form

  1. #1
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    Write your answer in a + bi form

    Find (2+3i)-(-5+8i)

    also

    Find (5-9i)(2+3i)
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  2. #2
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    e^(i*pi)'s Avatar
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    Quote Originally Posted by Mhockey02 View Post
    Find (2+3i)-(-5+8i)

    also

    Find (5-9i)(2+3i)
    When adding or subtracting complex numbers add/subtract the real component and the imaginary component separately

    (a+bi)-(c+di) = (a-c) + (b-d)i


    When multiplying treat it the same as you would with any polynomial. Just recall that i^2 = -1
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  3. #3
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    So the answer for the first one is -4 and the second one is 9?
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  4. #4
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    Quote Originally Posted by Mhockey02 View Post
    So the answer for the first one is -4 and the second one is 9?
    No, there are no imaginary terms in your answers.

    For your first one: (2+3i)-(-5+8i) = (2-(-5)) + (3-8)i = 7-5i
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