Answer: y=-2cos(2(x+pi))-1, third choice
This is an upside down cosine max 1, min -3, period pi. So this is -2cos(2x) -1 which is equivalent to the chosen one; adding 2pi to the angle doesn't change the value of the trig function. The factor of 2 on the outside gives the range of plus or minus two, subtracting 1 gets in the right y strip. The period of cosine is 2pi so the factor of 2 on x inside scales that to pi as required.
