RMS calculation of digitized periodic signal

I am calculating the RMS of a digitized periodic signal with 250 x data points per cycle. (1) Is the equation, SQRT((1/n)*(x1^2+x2^2+?+xn^2)), where n is 250? (2) How does this equation work if the signal has both positive and negative excursions?

tnx
GE

1) Yes
2) each point is squared, as you can see..

Being each point is squared, the negative points would become positive. Then summed makes the number larger. Never appreciated that fact before.