English: The two triangles are similar (but not congruent) because the angles are the same. For line 1, the "run" is negative, as shown. Setting the ratios equal yields Therefore
The person who associated a work with this deed has dedicated the work to the public domain by waiving all of their rights to the work worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law. You can copy, modify, distribute and perform the work, even for commercial purposes, all without asking permission.
http://creativecommons.org/publicdomain/zero/1.0/deed.enCC0Creative Commons Zero, Public Domain Dedicationfalsefalse
Captions
Proof that slopes obeying <math>m-1m_2=-1</math> imply perpendicular lines