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A hovercraft takes off from a platform.
Its height (in meters), 
x seconds after takeoff, is modeled by

h(x)=-(x-11)(x+3)
How many seconds after takeoff will the hovercraft land on the ground?
seconds

A hovercraft takes off from a platform. Its height (in meters), x x seconds after takeoff, is modeled by h(x)=(x11)(x+3) h(x) = -(x-11)(x+3) How many seconds after takeoff will the hovercraft land on the ground? seconds \text{seconds}

Full solution

Q. A hovercraft takes off from a platform. Its height (in meters), x x seconds after takeoff, is modeled by h(x)=(x11)(x+3) h(x) = -(x-11)(x+3) How many seconds after takeoff will the hovercraft land on the ground? seconds \text{seconds}
  1. Given height function: We are given the height function h(x)=(x11)(x+3)h(x) = -(x-11)(x+3). To find out when the hovercraft will land on the ground, we need to determine when the height h(x)h(x) is equal to 00.
  2. Set height function equal: Set the height function equal to zero and solve for xx:0=(x11)(x+3)0 = -(x-11)(x+3)
  3. Expand and simplify equation: Expand the equation: 0=x23x+11x+330 = -x^2 - 3x + 11x + 33
  4. Solve quadratic equation: Simplify the equation by combining like terms: 0=x2+8x+330 = -x^2 + 8x + 33
  5. Substitute values into formula: To find the xx values when the hovercraft is on the ground, we need to solve the quadratic equation x2+8x+33=0-x^2 + 8x + 33 = 0. This can be done by factoring, completing the square, or using the quadratic formula. Since the equation does not factor easily, we will use the quadratic formula: x=b±b24ac2ax = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a}, where a=1a = -1, b=8b = 8, and c=33c = 33.
  6. Calculate discriminant: Substitute the values of aa, bb, and cc into the quadratic formula:\newlinex=8±824(1)(33)2(1)x = \frac{{-8 \pm \sqrt{{8^2 - 4(-1)(33)}}}}{{2(-1)}}
  7. Calculate square root: Calculate the discriminant (the part under the square root):\newlineDiscriminant = 824(1)(33)=64+132=1968^2 - 4(-1)(33) = 64 + 132 = 196
  8. Substitute square root: Take the square root of the discriminant: 196=14\sqrt{196} = 14
  9. Calculate possible solutions: Substitute the square root back into the quadratic formula:\newlinex=8±142x = \frac{{-8 \pm 14}}{{-2}}
  10. Identify meaningful solution: Calculate the two possible solutions for xx:x1=(8+14)2=62=3x_1 = \frac{{(-8 + 14)}}{{-2}} = \frac{6}{{-2}} = -3x2=(814)2=222=11x_2 = \frac{{(-8 - 14)}}{{-2}} = \frac{-22}{{-2}} = 11
  11. Identify meaningful solution: Calculate the two possible solutions for xx:x1=(8+14)/2=6/2=3x_1 = (-8 + 14) / -2 = 6 / -2 = -3x2=(814)/2=22/2=11x_2 = (-8 - 14) / -2 = -22 / -2 = 11Since time cannot be negative, the solution x=3x = -3 seconds is not physically meaningful for this problem. Therefore, the hovercraft will land on the ground 1111 seconds after takeoff.

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