i am reading a book called "electronic principles and applications" by john pratley. there is a question in the exercise part that i am stuck on.

6. a steeped a.c wave has teh following values over equal intervals of time

value 4 6 6 4 2 0 0 -2 -4

time 0-1 1-2 2-3 3-4 4-5 5-6 6-7 7-8 8-9

I thought that the rms of a sine wave, not that this is a sine wave, would be 0.707 x max value, 0.707 x 6 which is not the answer. i looked at the answer which is 3.74 and * 1.414 to get 5.28.

i did this in excel to help me find the answer.

the exercise questions cover information from chapters: peak to peak values, average or mean value of an alternating waveform, rms of an alternating waveform.

some of the questions in the exercises are a little confusing as none of the information has been covered yet. i also googled this question and found that it was taken from a different book by a different writer, or the other way round (plagarism)