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Math Help - problem solving area equation using pi

  1. #1
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    problem solving area equation using pi

    Hi all,

    I am having some trouble solving a basic area equation. I have the values and the answer but am unable to recreate it myself. This is a problem as I need to apply the same equation to solve my own values (smaller 2's indicate squared, I couldn't find the symbol for this, nor for pi):

    Area (km2) = pi(D/d)2

    Where D= 2.5, d=0.5. The answer I have for this is 4.9 km2.

    The equation I need to solve is for:

    pi(14/7)2


    Any help would be appreciated. I have tried a combination of things like pi x (D/d
    2), the squared inside and outside the bracket but am getting nowhere...

    Thanks in advance,

    E
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  2. #2
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    Re: problem solving area equation using pi

    Quote Originally Posted by glxej View Post
    Hi all,

    I am having some trouble solving a basic area equation. I have the values and the answer but am unable to recreate it myself. This is a problem as I need to apply the same equation to solve my own values (smaller 2's indicate squared, I couldn't find the symbol for this, nor for pi):

    Area (km2) = pi(D/d)2

    Where D= 2.5, d=0.5. The answer I have for this is 4.9 km2.

    The equation I need to solve is for:

    pi(14/7)2


    Any help would be appreciated. I have tried a combination of things like pi x (D/d
    2), the squared inside and outside the bracket but am getting nowhere...

    Thanks in advance,

    E
    Please post the entire problem.
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  3. #3
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    Re: problem solving area equation using pi

    Quote Originally Posted by glxej View Post
    Hi all,

    I am having some trouble solving a basic area equation. I have the values and the answer but am unable to recreate it myself. This is a problem as I need to apply the same equation to solve my own values (smaller 2's indicate squared, I couldn't find the symbol for this, nor for pi):

    Area (km2) = pi(D/d)2

    Where D= 2.5, d=0.5. The answer I have for this is 4.9 km2.

    The equation I need to solve is for:

    pi(14/7)2


    Any help would be appreciated. I have tried a combination of things like pi x (D/d
    2), the squared inside and outside the bracket but am getting nowhere...

    Thanks in advance,

    E
    \pi \left(\dfrac{14}{7}\right)^2 = 4\pi

    Which is just a number.

    Please post the entire problem
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  4. #4
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    Re: problem solving area equation using pi

    Sorry, not quite sure what is meant by the 'entire problem'. The above is all I have to work with....unless you mean the units for D and d, which are both in km.
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  5. #5
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    Re: problem solving area equation using pi

    Quote Originally Posted by glxej View Post
    The equation I need to solve is for:
    pi(14/7)2
    That is NOT an equation; all equations have an equal sign.
    Most of us here like to help, but NOT to "guess"...get my drift?

    If you're trying to evaluate that expression, then:
    pi times (14/7) to the power 2
    = 3.141... times 2 to the power 2
    = 3.141... times 4
    = 12.564...

    On this one:
    > Area (km2) = pi(D/d)2
    > Where D= 2.5, d=0.5. The answer I have for this is 4.9 km2.
    3.141... * (2.5/.5)^2 = 3.141... * 5^2 = 3.141... * 25 = 78.525...
    Your 4.9 makes no sense whatsoever...

    WHAT are you trying to do? WHERE does that "formula" come from?
    WHAT are D and d ? Are you working with circles (area pi * r^2) ?
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  6. #6
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    Re: problem solving area equation using pi

    Alright, so I am trying to work out the Topographic Area (A) (km2) knowing two diameters (D) and (d) both in km.

    The formula is from an academic scientific journal, I am trying to use their values to recreate their answer, and so that I may apply it to my own problem. However, I am unable to get the same answer which poses problems as the value is used later on in other formulas,

    The formula is:
    Area (km2) = pi(D/d)2

    Their application:
    Area (km2) = pi(2.5/0.5)2 = 4.9 km2

    Or another:
    Area (km2) = pi(9/5)2 = 64 km2

    I would like to apply it to:
    Area (km2) = pi(14/7)2 = ? km2

    Again, I cannot get the answer they get!? Any ideas how to solve this?

    (ps. Strangely, the next equation I am needed to was to work out the Structure Area (Sa). They use pretty much the same formula;
    Sa (km2) = pi(d/2) (again d=km)
    so for example, Sa (km2) = pi*(0.5/2)=~0.2km2 ....I am able to get the answer myself and it matches their values, but why not for the first formula!!)
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  7. #7
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    Re: problem solving area equation using pi

    Here's roughly what you're saying:

    3 * 5 = 15

    "they" have 3 * 5 = 60

    any idea how "they" got that?

    ANSWER: no idea
    Last edited by Wilmer; August 20th 2011 at 01:01 PM.
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  8. #8
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    Re: problem solving area equation using pi

    Quote Originally Posted by glxej View Post
    Alright, so I am trying to work out the Topographic Area (A) (km2) knowing two diameters (D) and (d) both in km.

    The formula is from an academic scientific journal, I am trying to use their values to recreate their answer, and so that I may apply it to my own problem. However, I am unable to get the same answer which poses problems as the value is used later on in other formulas,

    The formula is:
    Area (km2) = pi(D/d)2

    Their application:
    Area (km2) = pi(2.5/0.5)2 = 4.9 km2
    No, 2.5/.5= 5, 5^2= 25 and 25pi= 25(3.14)= 78.5

    Or another:
    Area (km2) = pi(9/5)2 = 64 km2
    Again, no. 9/5= 1.8. 1.8^2= 3.24, and pi(3.24)= 10.17

    However, the whole problem makes no sense if R and r are radii, measured in km, the "R/r" has no units. multiplying by pi will NOT give an area in "square kilometers".

    I would like to apply it to:
    Area (km2) = pi(14/7)2 = ? km2

    Again, I cannot get the answer they get!? Any ideas how to solve this?

    (ps. Strangely, the next equation I am needed to was to work out the Structure Area (Sa). They use pretty much the same formula;
    Sa (km2) = pi(d/2) (again d=km)
    so for example, Sa (km2) = pi*(0.5/2)=~0.2km2 ....I am able to get the answer myself and it matches their values, but why not for the first formula!!)
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  9. #9
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    Re: problem solving area equation using pi

    Quote Originally Posted by glxej View Post
    pi*(0.5/2)=~0.2km2 ....I am able to get the answer myself and it matches their values,...
    Huh? 3.14 * (.05/2) = 3.14 * .025 = ~.0785
    Are you joking around?
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