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A school plans to fence a rectangular playground with an area of 600 m². The length of the playground is 5 metres more than its width. (a) Form a quadratic equation representing the situation. (b) Solve the equation by completing the square. (c) Find the dimensions of the playground.

Mathematics

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3 parts
a

w2+5w−600=0w^2 + 5w - 600 = 0

b

w=−5+5972 or w=−5−5972w = \frac{-5 + 5\sqrt{97}}{2} \text{ or } w = \frac{-5 - 5\sqrt{97}}{2}

c

−5+5972 m\frac{-5 + 5\sqrt{97}}{2}\,m

5+5972 m\frac{5 + 5\sqrt{97}}{2}\,m

Step-by-step solution

10 steps

Here's the solution to the quadratic equations problem:

Part a· 2 steps

Form a quadratic equation representing the situation.

  1. Define variables.

    Let the width of the rectangular playground be ww meters.
    The length of the playground is 5 meters more than its width, so the length l=w+5l = w + 5 meters.
    The area of the playground is given as 600 m2600\,m^2.

  2. Form the equation.

    The area of a rectangle is given by the formula Area=length×widthArea = length \times width.
    Substitute the expressions for length, width, and the given area:

    600=(w+5)×w600 = (w + 5) \times w 600=w2+5w600 = w^2 + 5w

    Rearrange the equation into the standard quadratic form ax2+bx+c=0ax^2 + bx + c = 0:

    w2+5w−600=0w^2 + 5w - 600 = 0

    The quadratic equation representing the situation is w2+5w−600=0\boxed{w^2 + 5w - 600 = 0}.

Part b

w=−5+5972 or w=−5−5972w = \frac{-5 + 5\sqrt{97}}{2} \text{ or } w = \frac{-5 - 5\sqrt{97}}{2}

Solve the equation by completing the square.

  1. Isolate the variable terms.

    Start with the equation from part (a):

    w2+5w−600=0w^2 + 5w - 600 = 0

    Move the constant term to the right side of the equation:

    w2+5w=600w^2 + 5w = 600
  2. Complete the square.

    To complete the square for w2+5ww^2 + 5w, take half of the coefficient of ww (which is 5), square it, and add it to both sides of the equation.
    Half of 5 is 52\frac{5}{2}.
    Squaring it gives (52)2=254(\frac{5}{2})^2 = \frac{25}{4}.

    w2+5w+254=600+254w^2 + 5w + \frac{25}{4} = 600 + \frac{25}{4}
  3. Factor the left side and simplify the right side.

    The left side is now a perfect square trinomial:

    (w+52)2=24004+254\left(w + \frac{5}{2}\right)^2 = \frac{2400}{4} + \frac{25}{4} (w+52)2=24254\left(w + \frac{5}{2}\right)^2 = \frac{2425}{4}
  4. Take the square root of both sides.

    w+52=±24254w + \frac{5}{2} = \pm\sqrt{\frac{2425}{4}} w+52=±24252w + \frac{5}{2} = \pm\frac{\sqrt{2425}}{2}

    Note that 2425=25×97=597\sqrt{2425} = \sqrt{25 \times 97} = 5\sqrt{97}.

    w+52=±5972w + \frac{5}{2} = \pm\frac{5\sqrt{97}}{2}
  5. Solve for ww.

    Subtract 52\frac{5}{2} from both sides:

    w=−52±5972w = -\frac{5}{2} \pm \frac{5\sqrt{97}}{2} w=−5±5972w = \frac{-5 \pm 5\sqrt{97}}{2}

    The solutions to the equation are w=−5+5972 or w=−5−5972\boxed{w = \frac{-5 + 5\sqrt{97}}{2} \text{ or } w = \frac{-5 - 5\sqrt{97}}{2}}.

Part c

−5+5972 m\frac{-5 + 5\sqrt{97}}{2}\,m

Find the dimensions of the playground.

  1. Choose the valid value for width.

    From part (b), we have two possible values for ww:
    w1=−5+5972w_1 = \frac{-5 + 5\sqrt{97}}{2}
    w2=−5−5972w_2 = \frac{-5 - 5\sqrt{97}}{2}
    Since width cannot be a negative value, we must choose the positive solution.
    97≈9.8488\sqrt{97} \approx 9.8488.
    w1=−5+5(9.8488)2=−5+49.2442=44.2442≈22.122 mw_1 = \frac{-5 + 5(9.8488)}{2} = \frac{-5 + 49.244}{2} = \frac{44.244}{2} \approx 22.122\,m.
    w2=−5−5(9.8488)2=−5−49.2442=−54.2442≈−27.122 mw_2 = \frac{-5 - 5(9.8488)}{2} = \frac{-5 - 49.244}{2} = \frac{-54.244}{2} \approx -27.122\,m.
    Therefore, the width w=−5+5972 mw = \frac{-5 + 5\sqrt{97}}{2}\,m.

  2. Calculate the length.

    The length l=w+5l = w + 5.

    l=(−5+5972)+5l = \left(\frac{-5 + 5\sqrt{97}}{2}\right) + 5

    To add 5, express it with a denominator of 2: 5=1025 = \frac{10}{2}.

    l=−5+5972+102l = \frac{-5 + 5\sqrt{97}}{2} + \frac{10}{2} l=−5+597+102l = \frac{-5 + 5\sqrt{97} + 10}{2} l=5+5972 ml = \frac{5 + 5\sqrt{97}}{2}\,m
  3. State the dimensions.

    The dimensions of the playground are:
    Width: −5+5972 m\boxed{\frac{-5 + 5\sqrt{97}}{2}\,m}
    Length: 5+5972 m\boxed{\frac{5 + 5\sqrt{97}}{2}\,m}

    You've completed all your questions for today! Great work.

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