S-curve Graph Mirror

Hi All,

I have an s-curve equation that uses cosine. Any trigonometric function is allowed but I can't use exponential or logarithmic equations as they don't perform to what is required. The cosine equation works great for certain settings but for others, I need to mirror it using the existing coordinate points; I need to mirror the ess while using the same coordinate points. I've tried a few ways but I can't have the equation switching its location to a different quadrant. The attached mcad_pic1.png shows the equation, the current s-curve in red, and the needed s-curve in green. Please help me to find a variation of the current equation or a different trigonometric equation that will enable the green s-curve.

Thank you. Gary