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What's the easiest way to show x=35 in this diagram?

enter image description here

I eventually figured it out by drawing in two lines and chasing angles:

enter image description here

However, this is a 10th grade question, so I'm sure there's an easier answer.

I sense that I've effectively re-proven some basic theorem about secants/chords.

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1 Answer 1

up vote 2 down vote accepted

This is the inscribed angle theorem.

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