SOLUTION: I used the equation, y=-6x^2+36x to model the flight of hitting a tennis ball. The problem asked when was the ball exactly 48 feet off the ground. I used the x-box to find that aft

Question 1030926: I used the equation, y=-6x^2+36x to model the flight of hitting a tennis ball. The problem asked when was the ball exactly 48 feet off the ground. I used the x-box to find that after two seconds after being hit, the ball was exactly 48 feet off the ground. Unfortunately, I only solved half of the problem because the ball will reach 48 feet again before it hit the ground. Please help.
Found 2 solutions by ikleyn, josmiceli:
Answer by ikleyn(52780) (Show Source): You can put this solution on YOUR website!
.
It would be good if you explain

1. What are the variables "y" and "x" in your equation. Is "x" the time or the horizontal coordinate?

2. What is the source of this equation? Where did you take it? Where is it came from?

I am asking because if "x" is the time and "y" is the height above the ground in feet (as I can conclude from your text),
then the equation is INCORRECT.
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Comment from student: x is the time and y is the feet above the ground and I got this from a test where I have to correct it.

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My responce: Then the first term in the right side of the equation y = + . . . should be instead of .

Answer by josmiceli(19441) (Show Source): You can put this solution on YOUR website!

You want 2 solutions for

( same equation )
Divide both sides by

Complete the square

Take the square root of both sides

There is a 2nd answer which you get by
taking the negative square root of 1 also:

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The ball is at 48 ft 2 sec after it is hit and
also at 48 ft 4 sec after it is hit
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Here's the plot:

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