1. E={x is belong to real #:tanx>=0}
2.
Let f1,f2,f3.....real #→[0,∞) be a collection of functions, for each n∈N, define
An(x) = {x belongs to real #,fn(x)=0}
We assume each An is countable.
a) Define a set
B={ x belongs to real#: f1(x)+f2(x)+....=0}
Is B a countable set?
b) Define another set
C= (x belongs to real #: (f1(x))(f2(x))....=0}
Is C a countable set?