$Ifuis$ a differentiable function $att=0$ satisfying $u(0)=($:$0,-8,5$:$),$

$u^{\text{'}}(0)=($:$0,1,-4$:$),$ evaluate $\frac{d}{dt}(u(t)f(t)){|}_t=0.$

The value $of\frac{d}{dt}(u(t)cos(t)){|}_t=0isa$