
I'm having trouble on this problem I don't know how to set it up. I know XO=2 and OB=6. I'd appreciate any hints.

I'm having trouble on this problem I don't know how to set it up. I know XO=2 and OB=6. I'd appreciate any hints.
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(The diameter is $2 + 8 = 10$, so the radius $OB = 5$, but that's not necessary to know.)
The product of the lengths of line segments created by intersecting chords is a constant, so $AX \cdot XB = CX \cdot XD$.
This means that $CX = 4,$ and $AC = \sqrt{4^2 + 2^2} = 2\sqrt{5}.$