Question 861872
Solve using derivatives - A dart is shot straight up from 1.5 metres above ground level. The distance (d), in metres, the dart is above the ground at time (t), in seconds is: 

 {{{d(t)= -4.9t^2 + 20t + 1.5}}}


1) What is the maximum height the dart reaches? I think this is 21.92 m
Already answered.
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2) for how many seconds is the dart in the air? 
From t = 0 until d(t) = 0 at impact.
 {{{d(t)= -4.9t^2 + 20t + 1.5 = 0}}}
*[invoke solve_quadratic_equation -4.9,20,1.5]
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Ignore the negative solution.
t =~ 4.155 seconds