If at every point of a certain curve , the slope of the tangent equals $${{ - 2x} \over y},$$ the curve is _______.

The Laplace transform of $$f(t)$$ is $$F(s).$$ Given $$F\left( s \right) = {\omega \over {{s^2} + {\omega ^2}}},$$ the final value of $$f(t)$$ is __________.

Figure, show two thyristors each rated $$500A$$ (continuous) sharing a load current. Current through thyristor $$y$$ is $$120A.$$ The current through thyristor $$x$$ will be nearly __________ $$A.$$

A three phase $$ac$$-to-$$dc$$ diode bridge rectifier is supplied from a three-phase, $$440V$$ source. The rectifier supplies a purely resistive load. The average $$dc$$ voltage across the load will be ___________ $$V$$.