The Three-Chord Lemma

​
angles BAC and DAC
∠BAC
≈
22.500°
∠DAC
≈
22.500°
AB
+
AD
≈
3.637
2
AC
cos[∠BAC]
=
2
AC
cos[∠DAC]
≈
3.637
Let AB, AC, and AD be three chords on a circle such that AC bisects
∠
BAD. Then
AB+AD=2ACcos(∠BAC)
.
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External Links

Three-Chord Lemma (Wolfram MathWorld)

Permanent Citation

Jay Warendorff
​
​"The Three-Chord Lemma"​
​http://demonstrations.wolfram.com/TheThreeChordLemma/​
​Wolfram Demonstrations Project​
​Published: March 7, 2011