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Math Help - can anyone help wth this polynomial equation?

  1. #1
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    can anyone help wth this polynomial equation?

    a cement walk of uniform width surrounds a rectangular pool that is 10m wide and 50m long. find the width of the walk if its area is 864 m squared.

    can you help please??
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    is up to his old tricks again! Jhevon's Avatar
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    Quote Originally Posted by pieman396 View Post
    a cement walk of uniform width surrounds a rectangular pool that is 10m wide and 50m long. find the width of the walk if its area is 864 m squared.

    can you help please??

    Umm... this is EXACTLY like the question i answered for you before, all you do is change the numbers up.

    see http://www.mathhelpforum.com/math-he...ra-2-help.html

    was there something you didn't understand about the method i used. you should say so if you don't get it
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  3. #3
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    my work for the problem.. can you tell me whats wrong??

    yeah but i did it the same way but i ended up with

    864=(2x+50)(2x+10)
    864=4x^2 +20x + 100x +500
    864=4x^2 + 120x +500...divided by 4
    216= x^2 +30x +125
    0= x^2 +30x -91

    but it can't be broken up into two binomials.
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  4. #4
    Forum Admin topsquark's Avatar
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    Quote Originally Posted by pieman396 View Post
    yeah but i did it the same way but i ended up with

    864=(2x+50)(2x+10)
    864=4x^2 +20x + 100x +500
    864=4x^2 + 120x +500...divided by 4
    216= x^2 +30x +125
    0= x^2 +30x -91

    but it can't be broken up into two binomials.
    I haven't checked the numbers to make sure you have the correct equation, but if it doesn't factor, simply use the quadratic formula:
    Given ax^2 + bx + c = 0 then
    x = [-b (+/-) sqrt{b^2 - 4ac}]/(2a)

    -Dan
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    ???

    i have no idea what mean... i'm completely lost... bu ti really need help because i have a test on this stuff tomorrow..
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    is up to his old tricks again! Jhevon's Avatar
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    Quote Originally Posted by pieman396 View Post
    yeah but i did it the same way but i ended up with

    864=(2x+50)(2x+10)
    864=4x^2 +20x + 100x +500
    864=4x^2 + 120x +500...divided by 4
    216= x^2 +30x +125
    0= x^2 +30x -91

    but it can't be broken up into two binomials.
    use the quadratic formula. do you know it?
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    ...

    no i have no idea what the quadractic formula is....
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  8. #8
    Forum Admin topsquark's Avatar
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    Quote Originally Posted by pieman396 View Post
    i have no idea what mean... i'm completely lost... bu ti really need help because i have a test on this stuff tomorrow..
    Quote Originally Posted by pieman396 View Post
    0= x^2 +30x -91
    Quote Originally Posted by topsquark View Post
    Given ax^2 + bx + c = 0 then
    x = [-b (+/-) sqrt{b^2 - 4ac}]/(2a)
    It means this:
    Compare the expressions:
    ax^2 + bx + c = 0
    x^2 + 30x - 91 = 0

    So a = 1, b = 30, c = -91

    Thus
    x = [-b (+/-) sqrt{b^2 - 4ac}]/(2a)

    x = [-(30) (+/-) sqrt{(30)^2 - 4(1)(-91)}]/(2(1))

    x = [-30 (+/-) sqrt{900 + 364}]/2

    x = [-30 (+/-) 35.5528]/2

    x = (-30 + 35.5528)/2 = 2.77639
    or
    x = (-30 - 35.5528)/2 = -32.7764

    If you haven't used the quadratic formula yet, then I suspect there is an error in deriving your equation.

    -Dan
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    is up to his old tricks again! Jhevon's Avatar
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    Quote Originally Posted by topsquark View Post
    It means this:
    Compare the expressions:
    ax^2 + bx + c = 0
    x^2 + 30x - 91 = 0

    So a = 1, b = 30, c = -91

    Thus
    x = [-b (+/-) sqrt{b^2 - 4ac}]/(2a)

    x = [-(30) (+/-) sqrt{(30)^2 - 4(1)(-91)}]/(2(1))

    x = [-30 (+/-) sqrt{900 + 364}]/2

    x = [-30 (+/-) 35.5528]/2

    x = (-30 + 35.5528)/2 = 2.77639
    or
    x = (-30 - 35.5528)/2 = -32.7764

    If you haven't used the quadratic formula yet, then I suspect there is an error in deriving your equation.

    -Dan
    Your equation seems correct to me pieman396, follow topsquark's method. you should just memorize the quadratic formula and remember that a is the coefficient of x^2 ALWAYS, b is the coefficient of x ALWAYS and c is the lone constant ALWAYS
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  10. #10
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    thanks... but can help me with another problem now...



    A rocket is launched from ground level with an initial vellcity of 83.3m/s. When will the ball reach a height of 294m??


    i'm supposed to use polynomial equations to figure this out to but the only way i know how to do it is with physics.
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  11. #11
    Forum Admin topsquark's Avatar
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    Quote Originally Posted by pieman396 View Post
    thanks... but can help me with another problem now...



    A rocket is launched from ground level with an initial vellcity of 83.3m/s. When will the ball reach a height of 294m??


    i'm supposed to use polynomial equations to figure this out to but the only way i know how to do it is with physics.
    If you have a new (unrelated) question, you should post it in a new thread.

    What's wrong with doing it by Physics?

    Set an origin at the ground, where the ball-rocket started and set +y upward. Then y0 = 0m, v0 = +83.3 m/s and a = -9.8 m/s^2.

    Thus
    y = y0 + v0*t + (1/2)a*t^2 <-- Polynomial in t!!

    y = 83.3t - 4.9t^2

    So when is y = 294 m?

    294 = 83.3t - 4.9t^2

    4.9t^2 - 83.3t + 294 = 0

    Since you've never seen the quadratic equation, let's multiply both sides of this by 10:
    49t^2 - 833t + 2940 = 0

    This looks like a terrible mess, but note that 833 and 2940 are multiples of 49. Thus we can factor a 49:
    49(t^2 - 17t + 60) = 0

    t^2 - 17t + 60 = 0

    (t - 12)(t - 5) = 0

    Thus
    t = 12 s or t = 5 s.

    -Dan
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