38.(2022•齐齐哈尔二模)ΔABC\Delta ABCΔABC的内角AAA,BBB,CCC的对边分别为aaa,bbb,ccc,且a(3sinB−cosC)=(c−b)cosAa({\sqrt{3}\sin B-\cos C})=({c-b})\cos Aa(3sinB−cosC)=(c−b)cosA.从下列①②这两个条件中选择一个补充在横线处,并作答. ①OOO为ΔABC\Delta ABCΔABC的内心; ②OOO为ΔABC\Delta ABCΔABC的外心. (1)求AAA; (2)若b=3b=3b=3,c=5c=5c=5,____,求ΔOBC\Delta OBCΔOBC的面积.