... triangle P1 P2Q. Hence, Y2 -Y, - Y4 -Y, QP2 - TP4 PiQ P3 T x2-x, x4 -x3 or - Therefore, P, and P2 determine the same slope as P3 and P, . Fig. 3-2 17 18 LINES [CHAP. ... slope 3 has a point-slope equation = 3. (6) Let 2 be the line through the points (3, - 1) and (2,3). Its slope is m = ~ = - - 3-( -1 ) 4 - - x-2 Y+l Y-3 2-3 -1 -4 . ... upward. Moreover, the slope is not affected by the order in which the points are given: - - - - - - In general, ~ - 2-6 4 4 Y,-Y1 Yl -Y2 1-4 -3 3’ x, -x, XI -x, Fig. 3-3 ...