Question 1110482
When the equation has the form {{{ y = a*x^2 + b*x + c }}}
then the x-value of the vertex ( either max or min )  is
located at {{{ x[v] = -b/(2a) }}}
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You are given:
{{{ h = -16t^2 + 64t }}}
{{{ t[max] = -64/(2*(-16)) }}}
{{{ t[max] = 64/32 }}}
{{{ t[max] = 2 }}} sec
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Plug this back into equation to get {{{ h[max] }}}
{{{ h[max] = -16*2^2 + 64*2 }}}
{{{ h[max] = -64 + 64*2 }}}
{{{ h[max] = 64 }}}
The maximum height is 64 ft
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check:
plot the equation:
{{{ graph( 400,400,-1,5, -10, 80, -16x^2 + 64x ) }}}
looks right