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Homework Help: Please HeLp with definite integral

  1. Jan 10, 2008 #1
    1. The problem statement, all variables and given/known data
    definite integrals (1 + 3x) dx from (-1,5)

    3. The attempt at a solution
    i keep getting 6+54 but it should be 6+36

    i think i might be using the wrong property

    or multiplying wrong: 3[(6/n)i](6/n)
  2. jcsd
  3. Jan 10, 2008 #2


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    If you show more of your working it will make it easier for us to help you...
    What do you get for the indefinite integral?
  4. Jan 10, 2008 #3
    If it helps, remember that
    [tex] \int^{b}_{a} x^n dx = { \left[ \frac{x^{n+1}}{n} \right] }^b_a [/tex].
    And as mda said, it would be helpful to know how your calculations look.
  5. Jan 11, 2008 #4
    the indefinite integral is " X + [tex]\frac{3}{2}[/tex]X[tex]^{2}[/tex] " and if you calculate it for 5 to -1 the answer must be 42
  6. Jan 11, 2008 #5
    If you integrate the function (3x+1) then it becomes (1.5x^2+x) where 5 is the upper limit and -1 is the lower. Sub in x=5 first, then minus the answer for x=-1 and you should end up with 42. When x=5 you should get 42.5, and when x=-1 you should get 0.5. Make sure that when you square -1 the calculator makes it 1, and does not leave it as -1 as some do.
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