Why is f not a function from R to R if

a) f(x)=1x?

f(x) is not well-defined because there are two distinct values assigned to each x.
f(0) is not defined.
f(x) is not defined for x

Question

Why is f not a function from R to R if
 
a) f(x)=1x?
 
 
		f(x) is not well-defined because there are two distinct values assigned to each x.
		f(0) is not defined.
		f(x) is not defined for x<0.
 
 
b) f(x)=x−−√?
 
 
		f(0) is not defined.
		f(x) is not defined for x<0.
		f(x) is not well-defined because there are two distinct values assigned to each x.

jhannybean · Answer

part b makes absolutely no sense to me.

anonymous · Answer

what does 
$$f(x)=1x$$ mean?