Metric spaces RXR how to prove?

R is real line, C is set of Complex numbers

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?
a. Show whether the Euclidean metric on RxR is a metric.

There is a definition for "metric". Check all 3 clauses of that definition in this particular case.

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