If we considered the Euclidean metric on RXR

a. Show whether the Euclidean metric on R

RXR is a metric.

b. Show whether the Euclidean metric on C

C is a metric.

c. Generalize the Euclidean metric to a set made up of all n-tuples of real numbers

X=R power n. Is this also true on C power n?

Can I get some direction on solving this proofs?