ds/dt=1/((1+t)/(1-t))*(-1*(1+t)-(1+t)/(1-t)^2)
ds/dt(3)=1/((1+3)/(1-3))*(-1*(1+3)/(1-3)^2)=
=-(1/2)*(-4)=2
ds/dt=1/((1+t)/(1-t))*(-1*(1+t)-(1+t)/(1-t)^2)
ds/dt(3)=1/((1+3)/(1-3))*(-1*(1+3)/(1-3)^2)=
=-(1/2)*(-4)=2