SOLUTION: Benny and Jenny are identical twins. They are both the same height. Benny is standing 15 feet away from Jenny. He throws a ball to her and the highest height the ball reaches is 10

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Question 1124861: Benny and Jenny are identical twins. They are both the same height. Benny is standing 15 feet away from Jenny. He throws a ball to her and the highest height the ball reaches is 10 feet before she catches it. Sketch a graph and write an equation that models the path of the ball.
Answer by ankor@dixie-net.com(22740) About Me  (Show Source):
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Benny and Jenny are identical twins.
They are both the same height. Benny is standing 15 feet away from Jenny.
He throws a ball to her and the highest height the ball reaches is 10 feet before she catches it.
Sketch a graph and write an equation that models the path of the ball.
:
+graph%28+300%2C+200%2C+-6%2C+17%2C+-4%2C+15%2C+-.178x%5E2%2B2.67x%2C+10%29+
:
Derived the equation for this graph using the form ax^2 + bx = y
x=15; y=0
225a + 15b = 0
x=7.5; y=10, (axis of symmetry)
56.25a + 7.5b = 10
multiply by 2 and subtract from the 1st equation
225a + 15b = 0
112.5a +15b = 20
-------------------subtraction eliminates b, find a
112.5a + 0 = -20
a = -20/112.5
a = -.178
find b
-.178(225) + 15b = 0
-40 + 15b = 0
15b = 40
b = 40/15
b = 2.67
the equation
y = -.178x^2 + 2.67x; will result in the above graph