Which of the following functions is not onto

The function f(x)=3x+4 is onto as for y ∈R,fy−43=y The function f:R+→R+,f(x)=x is onto as for y∈R+, fy2=y⋅f:R→R+,f(x)=x2+2 is not onto as 1∈R+ has no pre-image.