$cos\widehat{x O y}=\frac{OA^2+OB^2-AB^2}{2.OA.OB}=\frac{-161}{800}$
$\Rightarrow \widehat{x O y} \approx 101,6^{\circ}$
$cos\widehat{x O y}=\frac{OA^2+OB^2-AB^2}{2.OA.OB}=\frac{-161}{800}$
$\Rightarrow \widehat{x O y} \approx 101,6^{\circ}$