One to one functions

[matrix_204]

i was just wondering, since there is no example in the book given, but if a problem asks u to find the k value of something like, f(x)=(x^3)/3+x^2+kx or f(x)=x^3+kx^2+x, how would i find the k value such that the function is one-one?
It would be helpful if someone can do an example?
thanks

[arildno]

You might try to utilize the fact that an (strictly) increasing (or decreasing) function is one to one.