Question 789312
{{{d=v[f] t - (1/2) a t^2}}}
{{{2d=2v[f] t -  a t^2}}}
{{{at^2-2v[f] t+2d= 0 }}}
Using the quadratic formula:
{{{t = (2v[f] +- sqrt((2v[f])^2-4*a*(2d) ))/(2*a) }}} ---> {{{t = (2v[f] +- sqrt(4v[f]^2-8ad ))/(2*a) }}}