Question

The hieght of a rocket above the ground is modelled by the quadratic function h(t) = -4t^2 + 32t, where h(t) is the height in metres, t seconds after the rocket was launched. a. How long will the rocket be in the air? How do you know? b. How high will the rocket be after 3s?

Answer 1

Solve for the zeroes of h(t), and from those you should have the time it lands. Plugging in 3 to h(3) will give you the height after 3 seconds.

Answer 2

Well I don't know if my procedure is right but the answer is correct:

a. h(t) = -4t^2 + 32t
0 = -4t^2 + 32t
-32t = -4t^2
----- ------
-4t -4t
8 = t

Answer 3

So to solve the zeros I use the factored form?

Answer 4

Yes, or the quadratic equation.

Answer 5

How do i use the factored form when it's f(x) = ax^2 + bx?

Answer 6

x = (-b +- sqrt(b^2 - 4 * a * c)) / (2 * a)

Answer 7

Plug in the coefficients and you should have the time(s) it is at ground level.

Answer 8

ohh, so I use the quadratic formula? But how about if I want to use the factored form?

Answer 9

-4t(t-8) is factored.

Answer 10

also to get c in the quadratic formula I must c= -b/2a? or c = (-b/2)^2

Answer 11

-4t(t-8) = 0 => t = 0, 8.

Answer 12

ohhhh.