Question 549675
{{{ h(t) = -9.8t^2 -10t +190 }}}
Note that if I make {{{ t = 0 }}}, which is
when the stone is thrown from the
top of the building, I get {{{ 190 }}} ft as I should:
{{{ h(0) = -9.8*0^2 -10*0 +190 }}}
{{{ h(0) = 190 }}}
The problem wants to know what is {{{t}}}
when {{{ h(t) = 0 }}}, or ground level.
{{{ 0 = -9.8t^2 -10t +190 }}}
Use the quadratic formula
{{{t = (-b +- sqrt( b^2-4*a*c ))/(2*a) }}} 
{{{ a = -9.8 }}}
{{{ b = -10 }}}
{{{ c = 190 }}}
{{{t = (-(-10) +- sqrt( (-10)^2-4*(-9.8)*190 ))/(2*(-9.8)) }}} 
{{{t = ( 10 +- sqrt( 100 + 4*(-9.8)*190 ))/(-19.6)) }}} 
{{{t = ( 10 +- sqrt( 100 + 4*(-9.8)*190 ))/(-19.6)) }}} 
I can't finish this because my cat, the Widster, just curled
up beside me, and I'm not going to disturb him to get a calculator.
But you get the idea.