Hi, can anyone help with this question, I can't get me head around power series.

A sound wave is given by the function:

$\displaystyle f(t) = 0.5e^{-2t} \cos 4t $

Write down the first four terms of the power series expansions of $\displaystyle e^{–2t}$and $\displaystyle cos 4t$

Determine the cubic (up to and including the third power oft) approximation off(t) and calculate the accurate and approximate values off(0.02) giving your results correct to 3 decimal places.

Thanks