【简答题】已知O为△ABC的外心,以线段OA、OB为邻边作平行四边形,第四个顶点为D,再以OC、OD为邻边作平行四边形,它的第四个顶点为H. (1)若 OA = a , OB = b , OC = c , OH = h ,试用 a 、 b 、 c 表示 h ; (2)证明: AH ⊥ BC ; (3)若△ABC的∠A=60°,∠B=45°,外接圆的半径为R,用R表示 | h | .
【简答题】填空 dress, throughout, offer, make up, advise 1. You'd better_______ in layers because it is very cold outside. 2. The old man__________ the children to read more books and get more knowledge. 3. There...