Q. 13.9( 96 Votes )

Show that the function f : R* R* defined by is one-one and onto, where R* is the set of all non-zero real numbers. Is the result true, if the domain R* is replaced by N with co-domain being same as R*?

Answer :

It is given that f : R* R* defined by

check for one-one:

For a function to be one-one, if f(x) = f(y) then x = y.

f(x) = f(y)



x = y


⇒Therefore,  f is one one.


We can see that y ϵ R, there exists , such that



f is onto.


Therefore, function f is one-one and onto.


Now, Let us consider g: N R* defined by



Then, we get,


g(x1) = g(x2)



x1 = x2


g is oneone.


It can be observed that g is not onto as for 1.2 ϵ R there does not exist any x in N such that



Therefore, function g is one –one but not onto.

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