Question 1200805
The height h metres of a ball at time t second after it is thrown up into the air Is given by the expression 
h= 1+ 15t - 5t^2
(i) Find the times at which the height is 11m
h= 1+ 15t - 5t^2 = 11
5t^2 - 15t + 10 = 0
t^2 - 3t + 2 = 0
(t-1)*(t-2) = 0
t = 1, t = 2 seconds.
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(ii) Use your calculator to find the time when the ball hits the ground
h= 1+ 15t - 5t^2 = 0

*[invoke solve_quadratic_equation -5,15,1]
Ignore the negative value.
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(iii) what is the greatest height the ball reaches
The vertex of the parabola is at t = -b/2a
t = -15/-10 = 1.5 seconds
h(1.5) = 12.25 meters