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Algebra
Pregunta

9. The height of a ball at a given time can be modelled with the quadratic function

$$h ( t ) = - 5 t ^ { 2 } + 20 t + 1$$ , where height, $$h ( t )$$ , is in metres and time, $$t$$ , is in seconds. How long is the ball in the air?

$$t = 2 + \sqrt { \frac { 21 } { 5 } }$$