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    The question is:

    Express: (1 + 2i)² + (3 - i)³ in the form a + bi.

    I get 15 - 24i, but the book gets 15 - 22i. I am fairly sure that I'll be wrong.

    Thank you.

    Ref: P4, Ex 3a, 3(d).
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    The book is right.
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    (Original post by samd)
    The question is:

    Express: (1 + 2i)² + (3 - i)³ in the form a + bi.

    I get 15 - 24i, but the book gets 15 - 22i. I am fairly sure that I'll be wrong.

    Thank you.

    Ref: P4, Ex 3a, 3(d).
    The book is right.
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    (Original post by samd)
    The question is:

    Express: (1 + 2i)² + (3 - i)³ in the form a + bi.

    I get 15 - 24i, but the book gets 15 - 22i. I am fairly sure that I'll be wrong.

    Thank you.

    Ref: P4, Ex 3a, 3(d).
    (1 + 2i)(1 + 2i) = 1 + 4i + 4i2
    = 4i - 3

    (3 - i)(3 - i)(3 - i) = (9 - 6i + i2)(3 - i)
    = 27 - 18i + 3i2 - 9i + 6i2 -i3
    = 18 - 26i

    Adding these gives 15 - 22i
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    (Original post by samd)
    The question is:

    Express: (1 + 2i)² + (3 - i)³ in the form a + bi.

    I get 15 - 24i, but the book gets 15 - 22i. I am fairly sure that I'll be wrong.

    Thank you.

    Ref: P4, Ex 3a, 3(d).
    With binomial theorem you get

    1 + 4i - 4 + 27 - 27i - 9 + i
    • Thread Starter
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    Thank you everyone.

    I tried to do it by the Bionomial but wrote (-i)3 as -i, when really it is -i x -i x -i => -1 x -i = i.

    Thanks again.
 
 
 
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