The difference is, that you could just continue using XP until Win7 was released or continue using Win7 until Win10 was released. Win10 will reach end of life next year and then the only supported Windows will be Windows 11. Vista or Win8 were never as forced as Win11 is now.
That requires neither engineering-level math nor paper nor patience. All you need is the chain rule and some basic knowledge of sine and cosine:
The derivative of cos is -sin, but because of the 6x you get an extra factor 6. The sine function is periodic on 2pi, so sin(6*2pi + pi/2) = sin(pi/2) = 1. So the result is -36