for two perpendicular lines with slopes m1, m2 , we have m1.m2 = -1.
now consider the x and y axes , their slopes are 0 and infinity , substituting :
0 times infinity = -1,
-1/0 = infinity.
but we know that -1/o = - infinity ,
so far , as 1 ≠ -1.
either zero = - zero ( which is always correct ).
infinity = - infinity
am I correct ....!