For each of the following functions, f : R → R, state whether they are one-to-one, onto, both, or neither. Use the following key: neither 1-1 nor onto, 1-1 but not onto, onto but not 1-1, both 1-1 and onto = bijective = invertible.
1. f(x) = x(x - 7)(x + 7)
2. f(x) = |x|
3. f(x) = sin(x)
4. f(x) = x^3 + 7
5. f(x) = x + 8|x|
6. f(x) = e^x
7. f(x) = x^2 + 3