Landon is standing in a hole that is 5.1 ft deep. He throws a rock, and it goes up into the air, out of the hole, and then lands on the ground above. The path of the rock can be modeled by the equation y = -0.005x2 + 0.41x - 5.1, where x is the horizontal distance of the rock, in feet, from Landon and y is the height, in feet, of the rock above the ground. How far horizontally from Landon will the rock land?
A. 66.71 ft
B. 33.35 ft
C. 15.29 ft
D. 7.65 ft
i think c

Question

Landon is standing in a hole that is 5.1 ft deep. He throws a rock, and it goes up into the air, out of the hole, and then lands on the ground above. The path of the rock can be modeled by the equation y = -0.005x2 + 0.41x - 5.1, where x is the horizontal distance of the rock, in feet, from Landon and y is the height, in feet, of the rock above the ground. How far horizontally from Landon will the rock land?
  A. 66.71 ft 	
  B. 33.35 ft 	
  C. 15.29 ft 	
  D. 7.65 ft
i think c

anonymous · Answer

The -0.005x2 is 0.005 times 2?

raven45 · Answer

huh?

anonymous · Answer

In the equation, the number "-0.005x2" is "-0.005 times 2"?

raven45 · Answer

so its c right

phi · Answer

$$  y = -0.005x^2 + 0.41x - 5.1 $$
they want the x value for when y is 0.
Because the rock comes out of a hole, the first time the rock reaches "ground level" (at y=0) does not count.

To find the answer, we solve for x in the equation
$$  -0.005x^2 + 0.41x - 5.1 =0 $$
and pick the bigger x.

I would use the quadratic formula.

anonymous · Answer

Is this in any way accurate?

anonymous · Answer

I didn't do this myself, by the way.

phi · Answer

that gives the first solution for when y=0.

but we want the other solution (take the negative of the square root)

raven45 · Answer

okay so it is c

phi · Answer

here is a picture
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