limx→∞[(3x-1)/(3x+4)]^(x+1)
=limx→∞[1-5/(3x+4)]^[(3x+4)/5*5/3+1/3]
=limx→∞[1-5/(3x+4)]^[-(3x+4)/5]^[-5/3]
=e^(-5/3)