(Solved):
For xR1 and yR1, define d1(x,y)=(xy)2,d2(x,y)=xy,d3(x,y)=x2y2 ...
For x?R1 and y?R1, define d1?(x,y)=(x?y)2,d2?(x,y)=?x?y??,d3?(x,y)=?x2?y2?,d4?(x,y)=?x?2y?,d5?(x,y)=1+?x?y??x?y??.? Determine, for each of these, whether it is a metric or not.