What are AC and DC Power respectively used for?

Space-time metric ds2= -dt2+at2dx2+bt2dy2+ct2dz2 (a)how does the area of a rectangle with vertices at ( x=0, y=0, z=0 ), (1,0,0 ), ( 0,1,0 ) and (1,1,0 ) changes with time? (b) if a photon moving in the x direction starts from the origin at t=1, when does it reach x=l? (ds=0 for the trajectory of a photon.) (c) the proper time for a particle is defined by cd=ds. what is the proper time for a particle to move along the trajectory ( x(t)=t, y(t)=0, z(t)=0 ) from t=0 to 1 ? what is the condition on the parameter a so that the velocity of the particle never exceeds the speed of light ?

Against his financial advisor's advice, frank has decided to invest his money in some risky stocks because he once made quite a bit of money in the stock market. his decision illustrates a. the representativeness heuristic b. overconfidence c. the availability heuristic d. confirmation bias select the best answer from the choices provided

Petroleum contains energy. a. light b. kinetic c. chemical d. mechanical