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Maths question help

  • 18-01-2012 9:06pm
    #1
    Irish Fox
    Closed Accounts Posts: 41 ✭


    i know i ask a lot of q's on this forum but oh well anyways
    i can't do this maths q but if i know how to do this one i can do them all

    write these products in the form a + bi

    (2+7i)(3-5i)

    3i(2+4i)

    thanks


Comments

  • #2
    Galway K9
    Registered Users, Registered Users 2 Posts: 2,353 ✭✭✭Galway K9


    (2+7i)(3-5i)


    3i(2+4i)

    2 * 3 + 2 * 5i * 7i * 3 - 7i * 5I
    6 +10i * 21i - 35i2
    Have guess at rest ill post rest tomorrow as on phone and Pain


  • #3
    TheMathsTutor
    Closed Accounts Posts: 44 ✭TheMathsTutor


    Previous answer is incorrect - it has several mistakes.

    I'll give you a start on the first one, and a hint, but if you don't mind, I won't do the whole thing for you as you will learn more by doing it yourself:

    (2+7i)(3-5i)

    = 2(3-5i) +7i(3-5i)

    Hint:
    Now multiply each of those terms outside the brackets by the terms of the expressions inside the brackets.

    As for 3i(2+4i), this one is easier. Multiply the term outside the brackets by the terms of the expression inside the brackets.

    And remember, i^2 (meaning i squared) = -1

    Hope it helps


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