Can someone explain to me how to recongnize functions so i can stop asking?

If 2(a^2+b^2)=(a+b)^2 then, > a+b=0, > ab=0, > a=b, > 2a=b

1yd 1 ft = 1 1/12 1 1/3 1 1/2 1 1/6

Apassenger train and a freight train leave san jose at 3pm, traveling in the same direction. the passenger train is going three times as fast as the freight train. at 6pm they are 240 miles apart. how fast is each travelling? explain your answer and show your