We looked at periodic functions.
Started most problems by finding the amplitude and the period.
The amplitude is basically the absolute value of the coefficient multiplying the function. If there is no number, the amplitude of a sine or cosine function is 1.
The amplitude can be found by 2π/# the number in front of the x, as in cos(2x) the # is 2.
After that, you should know the basic shape of the sine and cosine functions. You can graph two periods (for this set of problems) and fill in the zeros.