Answer:
Part a) About 48.6 feet
Part b) About 8.3 feet
Part c) The domain is
and the range is ![0 \leq y \leq 8.3\ ft](https://tex.z-dn.net/?f=0%20%5Cleq%20y%20%5Cleq%208.3%5C%20ft)
Step-by-step explanation:
we have
![y=-0.014x^{2} +0.68x](https://tex.z-dn.net/?f=y%3D-0.014x%5E%7B2%7D%20%2B0.68x)
This is a vertical parabola open downward (the leading coefficient is negative)
The vertex represent a maximum
where
x is the ball's distance from the catapult in feet
y is the flight of the balls in feet
Part a) How far did the ball fly?
Find the x-intercepts or the roots of the quadratic equation
Remember that
The x-intercept is the value of x when the value of y is equal to zero
The formula to solve a quadratic equation of the form
is equal to
![x=\frac{-b(+/-)\sqrt{b^{2}-4ac}} {2a}](https://tex.z-dn.net/?f=x%3D%5Cfrac%7B-b%28%2B%2F-%29%5Csqrt%7Bb%5E%7B2%7D-4ac%7D%7D%20%7B2a%7D)
in this problem we have
![-0.014x^{2} +0.68x=0](https://tex.z-dn.net/?f=-0.014x%5E%7B2%7D%20%2B0.68x%3D0)
so
![a=-0.014\\b=0.68\\c=0](https://tex.z-dn.net/?f=a%3D-0.014%5C%5Cb%3D0.68%5C%5Cc%3D0)
substitute in the formula
![x=\frac{-0.68(+/-)\sqrt{0.68^{2}-4(-0.014)(0)}} {2(-0.014)}](https://tex.z-dn.net/?f=x%3D%5Cfrac%7B-0.68%28%2B%2F-%29%5Csqrt%7B0.68%5E%7B2%7D-4%28-0.014%29%280%29%7D%7D%20%7B2%28-0.014%29%7D)
![x=\frac{-0.68(+/-)0.68} {(-0.028)}](https://tex.z-dn.net/?f=x%3D%5Cfrac%7B-0.68%28%2B%2F-%290.68%7D%20%7B%28-0.028%29%7D)
![x=\frac{-0.68(+)0.68} {(-0.028)}=0](https://tex.z-dn.net/?f=x%3D%5Cfrac%7B-0.68%28%2B%290.68%7D%20%7B%28-0.028%29%7D%3D0)
![x=\frac{-0.68(-)0.68} {(-0.028)}=48.6\ ft](https://tex.z-dn.net/?f=x%3D%5Cfrac%7B-0.68%28-%290.68%7D%20%7B%28-0.028%29%7D%3D48.6%5C%20ft)
therefore
The ball flew about 48.6 feet
Part b) How high above the ground did the ball fly?
Find the maximum (vertex)
![y=-0.014x^{2} +0.68x](https://tex.z-dn.net/?f=y%3D-0.014x%5E%7B2%7D%20%2B0.68x)
Find out the derivative and equate to zero
![0=-0.028x +0.68](https://tex.z-dn.net/?f=0%3D-0.028x%20%2B0.68)
Solve for x
![0.028x=0.68](https://tex.z-dn.net/?f=0.028x%3D0.68)
![x=24.3](https://tex.z-dn.net/?f=x%3D24.3)
<em>Alternative method</em>
To determine the x-coordinate of the vertex, find out the midpoint between the x-intercepts
![x=(0+48.6)/2=24.3\ ft](https://tex.z-dn.net/?f=x%3D%280%2B48.6%29%2F2%3D24.3%5C%20ft)
To determine the y-coordinate of the vertex substitute the value of x in the quadratic equation and solve for y
![y=-0.014(24.3)^{2} +0.68(24.3)](https://tex.z-dn.net/?f=y%3D-0.014%2824.3%29%5E%7B2%7D%20%2B0.68%2824.3%29)
![y=8.3\ ft](https://tex.z-dn.net/?f=y%3D8.3%5C%20ft)
the vertex is the point (24.3,8.3)
therefore
The ball flew above the ground about 8.3 feet
Part c) What is a reasonable domain and range for this function?
we know that
A reasonable domain is the distance between the two x-intercepts
so
![0 \leq x \leq 48.6\ ft](https://tex.z-dn.net/?f=0%20%5Cleq%20x%20%5Cleq%2048.6%5C%20ft)
All real numbers greater than or equal to 0 feet and less than or equal to 48.6 feet
A reasonable range is all real numbers greater than or equal to zero and less than or equal to the y-coordinate of the vertex
so
we have the interval -----> [0,8.3]
![0 \leq y \leq 8.3\ ft](https://tex.z-dn.net/?f=0%20%5Cleq%20y%20%5Cleq%208.3%5C%20ft)
All real numbers greater than or equal to 0 feet and less than or equal to 8.3 feet