A model rocket is launched from a roof into a large field. The path of the rocket can be modleled by the equation y = -0.8x^2 + 12x + 25.8 where x is the horizontal distance, in meters, from starting point on the roof and y is the height, in meters, of the rocket above the ground.

How far horizontally from its starting point will the rocket land? Round your answer to the nearest hundredth?

Question

A model rocket is launched from a roof into a large field.  The path of the rocket can be modleled by the equation y = -0.8x^2 + 12x + 25.8 where x is the horizontal distance, in meters, from starting point on the roof and y is the height, in meters, of the rocket above the ground.

How far horizontally from its starting point will the rocket land?  Round your answer to the nearest hundredth?

anonymous · Answer

please don't type a reply and leave like other people I actually need help kind of walking through it so I can understand

jdoe0001 · Answer

http://openstudy.com/study#/updates/5344641ce4b0acf2f91c0b3b

ranga · Answer

When the rocket lands on the ground, its height above the ground, y,  will be zero.
Set y = 0 and solve for x.

jdoe0001 · Answer

there's an assumption you've covered solving quadratic equations, since this is a quadratic

anonymous · Answer

Yes kind of but I'm am not sure or have a clue how to do this one that's why I closed the last question because it was just an equation you gave me when I need help completing the steps

jdoe0001 · Answer

hmmm is really all you need to solve it, just set  y = 0,and solve for "x"
judging from the coefficients, I'd think you may need to use the quadratic formula

anonymous · Answer

I am not exactly sure what the quadratic formula is, I did all the homework for this unit and I am just dead in the water on this question for some reason

jdoe0001 · Answer

meaning you'd need to cover the section on quadratics first

jdoe0001 · Answer

http://www.youtube.com/watch?v=1Pva-Iv43Nc <--- solving by factoring and using the quadratic formula

ranga · Answer

$$\Large x = \frac{ -b \pm \sqrt{b ^{2} - 4ac} }{ 2a }\a = -0.8, b = 12, c = 25.8$$

anonymous · Answer

so 25.80 would be my answer if I worked it out right?

anonymous · Answer

ranga how exactly do I give you a medal?

ranga · Answer

How did you get 25.8 without plugging a,b and c values into the quadratic formula given above?

anonymous · Answer

wait a sec ill work it out

ranga · Answer

$$x = \Large \frac{ -12 \pm \sqrt{12 ^{2} - 4 * (-0.8) * 25.8} }{ 2* (-0.8) }$$

anonymous · Answer

-12-15.051/.16?

anonymous · Answer

My choices are or 25.80, or 37, or 17.24, or 16.91

ranga · Answer

$$x = \frac{ -12 \pm 15.052 }{ -1.6 }.~~~x = \frac{ -12 + 15.052 }{ -1.6 }~~or~~x= \frac{ -12 - 15.052 }{ -1.6 }$$

ranga · Answer

The first solution will give negative x which is not a valid solution.
Try the second solution:  $$x = \frac{-12-15.052}{-1.6} = \frac{-27.052}{-1.6} = 16.91$$