Ta có: \(\Delta OAB\) cân nên \(\widehat {OBA}=\widehat {OAB}\)
\(\Delta O'AC\) cân nên \(\widehat {O'CA}=\widehat {O'AC}\)
Mà \(\widehat {OAB}=\widehat {O'AC}\) (đối đỉnh)
\(\Rightarrow \widehat {OBA}=\widehat {OAB}=\widehat {O'AB}=\widehat {O'AC}\)
Nên \(\Delta OAB ∽ \Delta O'AC\;\;(g.g)\)
\(\Rightarrow \dfrac{OA}{O'A}=\dfrac{AB}{AC}\)
\(\Rightarrow AC=\dfrac{AB.O'A}{OA}=\dfrac{5.2}{3}=\dfrac{10}{3}\)
Vậy chọn \((A).\)
