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Anonymous
Anonymous asked in Science & MathematicsMathematics · 5 days ago

I don't understand what this math problem is asking for can someone help?

Consider the region bounded by the following graphs:

y = x^2 + 2x - 15, the x-axis, x=4 and x=7

what is the least number of integral needed to find the area of this region?

I have no idea what the question is asking can someone help or maybe give me steps. Thanks.

3 Answers

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  • 5 days ago
    Favorite Answer

    Only one integral is needed:

    the integral from x = 4 to x = 7 of

    (x^2 + 2x - 15) dx.

    After integration you have

    (1/3)x^3 + x^2 - 15x;

    plug in x = 7 and x = 4, you get

    (1/3)(343 - 64) + (49 - 16) - 15(7 - 4)

    = (1/3)(279) + 33 - 45

    = 81.

    Do check my arithmetic.

  • ?
    Lv 7
    5 days ago

    The wording of this question is very odd. If it's asking for the area of the region bounded by

              y = x² + 2x - 15

              x = 4

              x = 7

    This can be found by taking one integral:

                ₇                                                    ₇

              ∫  x² + 2x - 15 dx = (⅓ x³ + x² - 15x ⃒

              ⁴                                                      ⁴

                                         = 58.33 - (-22.67)

                                         = 81      ...................ANS

    Attachment image
  • 5 days ago

    draw it out. from the graph, you want the area under y = x² + 2x - 15 from 3 to 7, one integration.

    although that one integral is broken down into 3 using the rule ∫(a+b)du = ∫a du + ∫b du

    A = ∫ (x² + 2x - 15) dx   from 3 to 7

    A = (1/3)x³ + x² – 15x     from 3 to 7

    A = (1/3)7³ + 7² – 15•7  – ((1/3)3³ + 3² – 15•3)

    A = 343/3 + 49 – 105  – 9 – 9 + 45

    A = 114 1/3 – 29 = 85 1/3

    edit: missed the x= 4, but that just changes it a bit to

    A = (1/3)x³ + x² – 15x     from 4 to 7

    A = (1/3)7³ + 7² – 15•7  – ((1/3)4³ + 4² – 15•4)

    A = 343/3 + 49 – 105  – 64/3 – 16 + 60

    A = 279/3 – 12 = 81

    Attachment image
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