Question

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Real World: Choose ONE of the following quadratic equations to solve. State your method of solving, giving your reasoning for why you chose that method. Show all work, and put your final answers in context.

A person walking across a bridge accidentally drops an orange into the river below from a height of 140 ft. The equation 0=−x2+7x+18 gives the relationship between how many seconds, x, have passed when the orange hits the water. In how many seconds will the orange hit the water?
A bird drops a stick to the ground from a height of 80 feet. The equation 0=−16x2+64x+80 gives the number of seconds that have passed when it hits the ground. After about how many seconds did the stick hit the ground?
Things you MUST include: (1 point each for a total of 5 points)

Method of solving the quadratic.
Reasoning for choosing this method.
All work to solve the quadratic equation.
The two mathematical answers to the equation.
The answer to the question asked, based on which answer is reasonable.
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Answer 1

A bird drops a stick to the ground from a height of 80 feet. The equation 0=−16x2+64x+80 gives the number of seconds that have passed when it hits the ground. After about how many seconds did the stick hit the ground?

Explanation:

h = -16t^2 + 80 Stick hits the ground when h = 0:

0 = -16t^2 + 80

16t^2 = 80

t^2 = 80/16 = 5

t = POSITIVE root 5 (due to the real world nature of the problem)

t approximately 2.236 seconds.

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Graph is a downward opening parabola with h-intercept of 80, t-intercept(s) of sqrt(5), - sqrt(5)

Symmetric about h-axis, though I would only graph on the right side of the h-axis since

that is where t >= 0.