Question 1145445
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The fact that the ball reaches the height of 7 meters, means, according to the condition, that


    H = 7,  i.e.  2 + 13t - 5t^2 = 7.


Write it as a quadratic equation in the standard form


    -5t^2 + 13t - 5 = 0;


change the sign everywhere for your convenience


    5t^2 - 13t + 5 = 0


and apply the quadratic formula


    {{{t[1,2]}}} = {{{(13 +- sqrt(13^2-4*5*5))/(2*5)}}} = {{{(13 +- sqrt(69))/10}}}.


The roots are  {{{t[1]}}} = {{{(13-sqrt(69))/10}}} = 0.47 seconds  and  {{{t[2]}}} = {{{(13+sqrt(69))/10}}} = 2.13 seconds .    <U>ANSWER</U>
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