Question 998307: Consider the points A(-7, 10), B(12, 7), C(10, -24), and D(-8, -3). Which two lines determined by these points are perpendicular? Explain.
Answer by KMST(5328)   (Show Source):
You can put this solution on YOUR website! If two lines are perpendicular the product of their slopes is  .
With those 4 points, we can make
 rays, and
 lines.
We can calculate the slope of all those lines,
but that is a lot of work.
With some graph paper, to save time and effort, we could plot the 4 points and graph the 6 lines.
That would let us know which ones may be perpendicular,
and which definitely are not perpendicular.
Then, we can calculate the slopes of online the lines that might be perpendicular, and find which ones really are perpendicular.
 Lines AB and BC seem almost perpendicular, but AC and BD look perpendicular.
Let's check the slopes of AC and BD.
The slope of AC is
 .
The slope of BD is
 .
The product of the slopes is  ,
so AC and BD are indeed perpendicular.
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