[Ophatio]

ข้อ 13

$AP^2_2 = AP_3 \times AP_1 = 4\times 6 = 24$

$AP^2_1 = AP_2 \times AC $

$ AC = \frac{6^2}{\sqrt{24} } = 3 \sqrt{6} $

$AC^2 = AP_1 \times AB$

$AB = \frac{(3\sqrt{6})^2}{6} =9$