Question

how to tell if a relation is a function and give an example.

Answer 1

Ex: f: R ---> R
 f(x)=2x+1
    Definition:  For every value of x , exists only one value of f(x)
f(1)=2*1+1, f(1)=2*1+1=3
f(2)=2*2+1=4+1=5
......
f(100)=2*100+1=200+1=201