?????????????????????? "passing thru" ????????????????
???? yu must meen yu draw a kers that GO THRU a point
?????????????? "equashun for a chord" ???????????
draw thangs so the chord=horizontal line, then all yu need is leng & start point
????????????????? oa, ob, ab, pa, pb ????????????
??????????????????? "Sentree" ??????????????
me assume that be SENTER av serkel