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March 1st, 2019, 11:02 AM   #11
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Quote:
Originally Posted by paulm View Post
. . . first defining AB = 1.
As |BC| = |AB| - |AC|, |AC|/|AB| = |BC|/|AC| = (|AB| - |AC|)/|AC| = |AB|/|AC| - 1.
Multiplying by |AC|/|AB| gives (|AC|/|AB|)² = 1 - |AC|/|AB|, i.e. x² + x - 1 = 0, where x = |AC|/|AB|.

Thus it's convenient, but not essential, to let |AB| = 1.
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