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Ricardo throws a stone off a bridge into a river below.
The stone's height (in meters above the water), 
x seconds after Ricardo threw it, is modeled by

w(x)=-5(x-8)(x+4)
What is the maximum height that the stone will reach?
meters

Ricardo throws a stone off a bridge into a river below.\newlineThe stone's height (in meters above the water), xx seconds after Ricardo threw it, is modeled by\newlinew(x)=5(x8)(x+4)w(x)=-5(x-8)(x+4)\newlineWhat is the maximum height that the stone will reach?\newlinemetersmeters

Full solution

Q. Ricardo throws a stone off a bridge into a river below.\newlineThe stone's height (in meters above the water), xx seconds after Ricardo threw it, is modeled by\newlinew(x)=5(x8)(x+4)w(x)=-5(x-8)(x+4)\newlineWhat is the maximum height that the stone will reach?\newlinemetersmeters
  1. Determine Parabola Vertex: The maximum height of the stone corresponds to the vertex of the parabola described by the quadratic function w(x)=5(x8)(x+4)w(x) = -5(x - 8)(x + 4). Since the coefficient of the quadratic term is negative (5-5), the parabola opens downwards, and the vertex will give us the maximum height.
  2. Calculate Average of Roots: To find the vertex of the parabola, we need to determine the xx-coordinate of the vertex, which is the average of the roots of the quadratic equation. The roots are given by the factors (x8)(x - 8) and (x+4)(x + 4), which are x=8x = 8 and x=4x = -4, respectively.
  3. Find X-Coordinate of Vertex: Calculate the average of the roots to find the x-coordinate of the vertex:\newlinexx-coordinate of vertex = (8+(4))/2=4/2=2(8 + (-4)) / 2 = 4 / 2 = 2.
  4. Find Maximum Height: Now that we have the xx-coordinate of the vertex, we can find the maximum height by evaluating the function w(x)w(x) at x=2x = 2.\newlinew(2)=5(28)(2+4)w(2) = -5(2 - 8)(2 + 4).
  5. Evaluate Function at X=2X=2: Perform the calculations inside the parentheses first: w(2)=5(6)(6)w(2) = -5(-6)(6).
  6. Perform Final Calculation: Now multiply the numbers together to find the maximum height: w(2)=5×6×6=30×6=180w(2) = -5 \times -6 \times 6 = 30 \times 6 = 180.

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