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Commentary for "Perpendicular lines and the product of their slopes"

Ackbach

Indicium Physicus
Staff member
Jan 26, 2012
4,183
Your second method is very fast! I remember coming up with my own proof using vectors and dot products, but it took a whole page. Your second method, it seems to me, has a good deal of pedagogical value.
 
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MarkFL

Administrator
Staff member
Feb 24, 2012
13,735
Your second method is very fast! I remember coming up with my own proof using vectors and dot products, but it took a whole page. Your second method, it seems to me, has a good deal of pedagogical value.
Thank you...I stumbled upon that helping a student at another site to find the third vertex of a right triangle, when given two of the vertices in the plane, and the leg lengths. When I realized I had found a nice method to show the product of the slopes of perpendicular lines is -1, I raced here to add it to this topic. :D