Please help me to understand this problem:

Verify that the following function is a probability mass function, and determine the requested probabilities. f(x) = (512f?3)(1;'8)x I x= {1,2,3} Round your answers to four decimal places {e.g. 933654}. Is the fundion a probability mass function? (a)P(X51)=|:l (b: P001): |:| (c)P(21)= |:|