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More determinants!

  1. Jan 1, 2007 #1
    Everyone is going to start to hate me know because i keep asking so many questions, but really i do look around these boards to help someone, but the questions are to hard for me or someone answers before me! :redface:

    anyway my question is:

    If the determinant of

    a b c
    d e f
    g h i

    is 7

    then find the following determinants:

    a)

    a+2d b+2e c+2f
    d e f
    g h i

    b)

    a b c
    g h i
    d e f

    c)

    a b c
    d e f
    5g 5h 5i

    My Answer:

    i don't even know where to start!

    any tips?
     
  2. jcsd
  3. Jan 1, 2007 #2

    Hurkyl

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    Gold Member

    Those matrices bear resemblance to the original, don't they? ...
     
  4. Jan 1, 2007 #3
    yeah...
    i still don't know what to do...
     
  5. Jan 1, 2007 #4

    matt grime

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    Homework Helper

    You have been taught rules about how determinants change under row operations. Use them.
     
  6. Jan 1, 2007 #5
    wait, i wrote the question wrong (as usual, matt grime) the question is:

    a b c
    d e f
    g h 1

    is equal to 7

    the other parts are the same.

    if the question was the same as i had previously written it would i get:
    a) =7
    b) = -7
    c) =35
     
  7. Jan 1, 2007 #6

    radou

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    Homework Helper

    Looks correct.
     
  8. Jan 1, 2007 #7
    unfortunatley i wrote the question worng, in the book they replaced the i with 1...do you think that is a mistake?
     
  9. Jan 1, 2007 #8

    cristo

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    Staff Emeritus
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    Either way, it doesn't matter, since we don't need to know the actual value of i in order to compute the three determinants.
     
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