Browse Questions

# If $A=\{1,2,3\}$ and $B=\{2,3,4,9\}$, then which of the following is a function $f:A \;\rightarrow \;B$ ?

(A) $f(x)=x+1$
(B) $f(x)=2x$
(C) $f(x)=\sqrt x$
(D) $f(x)=x$

Ans: $f(x)=x+1$
Because if if $f(x)=2x$ then 3 has no image in B
If $f(x)=\sqrt x$ then none of the elements in A has image in B
If $f(x)=x$ then 1 has no image in B
If $f(x)=x+1$, then $f(1)=2,\:f(2)=3,\:f(3)=4$
edited May 18, 2014