Question

Show that a line through (0, 0) and (c, d) is perpendicular to a line through (0, 0) and (-d, c).

Slope of first line =

Slope of second line =

Answer 1

i really dont understand this

Answer 2

Slope for the first line is: (d-0)/(c-0) which is d/c.
Slope for the second line is: (c-0)/(-d-0) which is c/-d.
For two lines to be perpendicular, the multiplication of their slopes must be -1. i.e. d/c X c/-d which is -1. So they are perpendicular.
Any confusion?