Trigonometric functions
In y = a sin(b(x - c)) + d, the amplitude is |a|, the period is 2π/b, and d is the midline.
A worked example
For y = 5 cos(4x) + 2 the amplitude is 5 and the period is 2π/4 = 1.57, so the curve swings between 7 and -3.
The mistake people actually make
Multiply degrees by π/180 for radians, and set the calculator to the mode the question is written in. The period depends on b, not on the amplitude.