If completeness of a metric space is defined as,

A metric space is complete if every Cauchy sequence in M converges.

I am stuck trying to verify the following metric space is complete.

with the metric defined as

Cleary this is a metric space, but how can I see if its complete?

I thought a verification of completeness might be similar to testing whether the euclidean space is compete (that is with aid of the Bolzano Weierstrass theorem). But that theorem doesn't hold for general metric spaces.