math question

Question

A small toy rocket is launched from a 30-foot pad. The height (h, in feet) of the rocket t seconds after taking off is given by the formula
h= -2x² -4x + 30 

 

How long will it take the rocket to hit the ground?

Answer 1

OK, when the rocket hits the ground, the height is 0. We'll come up with two answers, one negative, which would be the portion of the parabola to the left of the y-axis, which doesn't exist in this situation. -2x - 4x + 30 = 0 First, to make things easier, I'm going to divide by -2, the common factor. x^2 + 2x - 15 = 0 (x + 5)(x - 3) = 0 x + 5 = 0 x = -5 Hey, here's that negative answer. Draw the parabola and it's cut off by the y-axis. This is the imaginary part. x - 3 = 0 x = 3 The rocket will hit the ground in 3 seconds. Pretty short flight!