m1 and m2 are the slope of two perpendicular lines, if
1 + m1.m2 = 0
m1 + m2 = 0
m1.m2 = 1
m1 = m2
RS is the chord of contact of the point P on a circle center at O. if m1=slope of ¯¯¯¯¯¯¯¯RS and m2=slope of ¯¯¯¯¯¯¯¯OP
Let L1 and L2 be two non-vertical lines with slopes m1 and m2 respectively. If α1 and α2 are the inclinations of lines L1 and L2, respectively. the acute angle (say θ) between lines L1 and L2 , is given by