this is a wierd question, two lines are perpendicular when the product of their slopes are -1, period. doesn't matter if they are nonvertical or not. what tools do you have to use in this proof?

ok, so we just do manipulations on the first equation so one side ends up looking like BD/DC, the other side should have some manipultions on m. here goes:

Now, this might be considered an algebra problem, but in the exercise I have to find the answer to:

Please let me know if I need to include more information or anything if this seems vague, it's probably an easy problem but I just don't understand how to get the correct answer, thanks.

-DC/BD = m ...............BD/DC is positive, so make that side positive

=> DC/BD = -m ..........i just multiplied through by -1

=> BD/DC = -1/m ........i took the inverse, so now one side looks like what we wanted and the other side tells us what it is in terms of m