Answer:
6.5 seconds
Step-by-step explanation:
Keep in mind that when
, this is the same height for both when the model rocket takes off and lands, so when the rocket lands, time is positive. Thus:

So, the amount of seconds that the model rocket stayed above the ground since it left the platform is 6.5 seconds
Answer:
sorry man can't help you with this one
The general form of a quadratic (second degree) equation is

, where

is called the Discriminant.
The Discriminant determines how many roots the equation will have as follows:
i) if D>0, the equation has 2 roots.
ii) if D=0, the equation has 1 double root.
iii) if D<0, the equation has no roots.
In our equation,

, a=1, b=-5, c=7
so the discriminant is D=(-5)^2-4*1*7=25-28<0
Thus the equation has no roots.
Remark: the equation has no roots in the Real numbers, but it has 2 roots in a larger set of numbers to be discussed in the future, the Complex numbers.