Did not understand the explanation for this answer - help

GRE Quant Problem Solving
1

Under Inscribed Polygon Problems II in prepswift.

Video says “AB is 48 degrees” - what does that mean? which exact angle is he referring to

I understand how the 120 and 72 came about, but got lost afterwards - anybody knows?

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2

Let O be the centre of the circle. The angle covered by BOA is 48 degrees.

3

thanks, got it

4

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While I understand this thread is solved, just sharing this visual in case it helps anyone.
My apologies for the poor handwriting and/or drawing.