Dont quite understand what my lecturer is wanting me to do with this question.. Don't know if i am trying to/thinking its more complicated then it actually is.

$\displaystyle

F(x) = x^3 + 2x+cos^2x

$

(a) Explain why there is a number x such that f(x) = 0

(b) Explain why there is only one value of x such that f(x) = 0

Thanks,