
◆ A little manipulation of the diagram
( as shown in the attachment )
Once you're done with this simple manipulation and the labeling, we get the equation : OB² + BC² = OC²
• r² = ( r - 9 )² + 15²
Solve this trivial equation to get : r = 17
• Radius = 17 is your final answer .
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Hope this helps you :)