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Math Help - area of a circle in a square

  1. #16
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    so its 707 to 0dp
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  2. #17
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    You're overdoing things!

    You need to practice with factors,
    then quadratics.

    Be very accustomed to those.
    Then you have Pythagoras' theorem to master.

    Firstly, zero multiplied by anything is zero...

    3(0)=0+0+0

    5(0)=0+0+0+0+0

    and so on...

    (R-3)(R-15)=0

    means R-3=0 or R-15=0

    So, from that, what possible values can we have for the radius ?
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  3. #18
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    well 3-3=0 and 15-15=0 so 3 and 15?
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  4. #19
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    Quote Originally Posted by kitobeirens View Post
    well 3-3=0 and 15-15=0 so 3 and 15?
    Yes, now does a radius of 3 make any sense, given that a side of the little rectangle is 6 ?
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  5. #20
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    no so is it 15
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  6. #21
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    Quote Originally Posted by kitobeirens View Post
    no so is it 15
    Yes, so plugging that R into the circle area equation gives the circle area
    as you have already done.

    I'd recommend you practice from the beginning with this problem.
    It would be of benefit to you.
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  7. #22
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    so the working oout i did before was right 225-270+45=0 which has r as 15
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  8. #23
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    so the area is 707
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  9. #24
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    Yes, in units of square centimetres, to the nearest square centimetre.
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  10. #25
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    how would you mathematically worked out r from r-15=0 and r-3=0 because it probably isn't great to guess that 3 is too small in other cases this might not be possible
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  11. #26
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    Quote Originally Posted by kitobeirens View Post
    how would you mathematically worked out r from r-15=0 and r-3=0 because it probably isn't great to guess that 3 is too small in other cases this might not be possible
    Given the geometry, R has to be greater than 6.
    So there is a lower bound for R as the problem was posed.
    Hence, this rules out the possiblity of R being 3.
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  12. #27
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    ok thanks for helping me
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  13. #28
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    If the 2 givens (3 and 6 in your case) are represented by u and v, and d = diameter of circle, then:

    d = [-b + SQRT(b^2 - 4c)] / 2, where b = -4(u + v) and c = 4(u^2 + v^2)

    Stick 3 and 6 in there and you'll get d = 30 (hence radius = 15).

    Try u=88, v=99: d = 638
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