Question 1181268

if {{{h=18}}} feet

{{{ 18=4+31t-16t^2 }}}.......solve for {{{t}}}

{{{ 0=-18+4+31t-16t^2 }}}
{{{ 0=-14+31t-16t^2 }}}
{{{ 0=-16t^2+31t -14}}}

use quadratic formula to calculate {{{t}}}

{{{t = (-b +- sqrt( b^2-4*a*c ))/(2*a) }}}.....you have {{{a=-16}}},{{{b=31}}},{{{c=-14}}}

{{{t = (-31 +- sqrt( 31^2-4*(-16)*(-14) ))/(2*(-16)) }}}

{{{t = (-31 +- sqrt( 961-896 ))/(-32) }}}

{{{t = (-31 +- sqrt( 65 ))/(-32) }}}


solutions:

{{{t = (-31 + sqrt( 65 ))/(-32) }}}=>{{{t =31/32 - sqrt( 65 )/32 }}}=>{{{t=0.72}}}
{{{t = (-31 - sqrt( 65 ))/(-32) }}}=> {{{t = 31/32 + sqrt( 65 )/32 }}}=>{{{t=1.22}}}