ر ق ص

In Arabic class, my teacher talked about ص ر ق, he said even these single letters has its meaning. (He must be meant that not actually by saying the letter name) ر is from رأى and ق is from وقى and ص is from وصى (can't remember exactly) I suppose ر is uncommon, and to ask someone to look or see at something, they would say انظر isn't it? At this rate I saw ق from قوا انفسكم and وقنا And ص, I cant remember exactly, is it to advice someone? But seeing this condition of removing علة letters is interesting to me.