Inherent Triangle Similarity

  •  Richard Kaufman    


This paper shows many relationships for a triangle by using its altitudes to form inner triangles that have a three 4-fold similarity. The altitudes partition the sides of the triangle $a={a_{1}}+{a_{2}},  b={b_{1}}+{b_{2}},  c={c_{1}}+{c_{2}}$ into partial side lengths of ${a_{1}},{a_{2}},{b_{1}},{b_{2}},{c_{1}},{c_{2}}$. We show that ${a_{1}b_{2}c_{1}}={a_{2}b_{1}c_{2}}$ and {\normalsize $c\left({c_{2}}-{c_{1}}\right)=b\left({b_{2}}-{b_{1}}\right)-a\left({a_{2}}-{a_{1}}\right)$. This latter equation can be written as {\normalsize ${c_{2}^{{2}}}-{c_{1}^{{2}}}=({b_{2}^{{2}}}-{b_{1}^{{2}}})-({a_{2}^{{2}}}-{a_{1}^{{2}}})$
or }{${a_{1}^{{2}}}+{b_{2}^{{2}}}+{c_{1}^{{2}}}={a_{2}^{{2}}}+{b_{1}^{{2}}}+{c_{2}^{{2}}}$}.
We also note that ${h_{1}h_{2}}={h_{3}h_{4}}={h_{5}h_{6}}$,
where ${h_{1}}+{h_{2}},{h_{3}}+{h_{4}},{h_{5}}+{h_{6}}$
are the altitudes of the triangle. These concise relationships for a triangle are based on its inherent similarity, and provide for simple equations, similar to the Pythagorean Theorem for right triangles.

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