Question 1687
a) yes,f is a function from R to R. Since forevery real x,there exists a unique
   f(x) corresponding to x.

b) No, since when x =0,f(0) is either 5 or -5(f(0) has no unique value.)

c)No,since x=0 causes the denominator to be zero,there is no value of f(0).