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Posted by on Monday, June 22, 2009 at 10:40pm.

Simplify: Write answers in the form of a + bi, where a and b are real numbers.

a. (1-2i)(1+3i)

b. (3-5i)(8-2i)

  • Algebra - , Monday, June 22, 2009 at 10:59pm

    Use FOIL to multiply them out.

  • Algebra - , Monday, June 22, 2009 at 11:15pm

    IS this correct, i notice that i^2 = -1 what does this mean?

    (1-2i)(1+3i)
    =1+3i-2i-6i^2
    =1+ i-6i^2
    = 1+i-6i

  • Algebra - , Monday, June 22, 2009 at 11:51pm

    no, 6i^2 is 6*(-1)
    so the last term is +6 and the final answer is
    7+i

  • Algebra - , Tuesday, June 23, 2009 at 12:11am

    So did I do any of this correct? What do I need to fix?

  • Algebra - , Tuesday, June 23, 2009 at 12:56am

    You have basically done it correctly, but omitted to change the sign of the last term because i2=-1

    (1-2i)(1+3i)
    =1+3i-2i-6i^2
    =1+ i-6i^2
    = 1+i +6i

  • Algebra - , Tuesday, June 23, 2009 at 12:57am

    Oops, it should read:

    (1-2i)(1+3i)
    =1+3i-2i-6i^2
    =1+ i-6i^2
    = 1+i +6
    =7+i

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