f(θ) = −1.75 cos(1/2(θ + 60°)) ; θ is in degrees.

This is a post that I did on  this topic  a year and a half ago :)

http://web2.0calc.com/questions/graphing-trig-functions_1#rr2

and here is another by Alan

http://web2.0calc.com/questions/can-anyone-remember-the-formulas-of-period-phase-shift-and-range-of-the-sin-function#r5

f(θ) = −1.75 cos(1/2(θ + 60°))   we can simplify this as

f(θ) = −1.75 cos([θ/2 + 30°]

The period is given by

θ/2   = 360°

θ = 720°

The amplitude is  =  abs [ -1.75]   = 1.75

Here's the graph :  https://www.desmos.com/calculator/7mhnsqww6c

Thanks, Melody, for that reference......