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tangents to circle from point

Source: LIMIT 2019 CAS2 P4

April 28, 2021
geometry

Problem Statement

From a point PP outside of a circle with centre OO, tangent segments PA\overline{PA} and PB\overline{PB} are drawn. If 1OA2+1PA2=116\frac1{\left|\overline{OA}\right|^2}+\frac1{\left|\overline{PA}\right|^2}=\frac1{16}, then AB=\left|\overline{AB}\right|=? <spanclass=latexbold>(A)</span> 4<span class='latex-bold'>(A)</span>~4 <spanclass=latexbold>(B)</span> 6<span class='latex-bold'>(B)</span>~6 <spanclass=latexbold>(C)</span> 8<span class='latex-bold'>(C)</span>~8 <spanclass=latexbold>(D)</span> 10<span class='latex-bold'>(D)</span>~10