Each side of a triangle is a chord of the same circumcircle.
WHAT HAPPENS IF…If A=B=60° and a=2, what are the other sides?
Interactive exploration
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Connect the picture to the ideasinAa=sinBb=sinCc=2R
A chord subtending an inscribed angle A has length 2R sinA. Applying this to each side produces the common ratio. The formula remains valid for obtuse angles because sine has the same value for supplementary angles.
A detail that matters
The side and angle in each ratio must be opposite one another.