math
posted by
rudy
.
im trying to take the derivative of this problem and plug in seven but im not getting the answer.
s=t3–2t2–6t t> or equal to 0
where s is measured in meters and t in seconds. When does the particle reach a velocity of 7 m/s?

math 
Reiny
ds/dt = 3t^2  4t  6
so when ds/dt = 7
3t^2  4t  6 = 7
3t^2  4t  13 = 0
Solve using the quadratic equation, and use the positive answer.
(I got 2.85 sec)

math 
stephen
if I am driving a car at 100km / hr and my reaction time is 0.382 seconds.
with many thanks Stephen