2014年江苏高考数学试卷第18题:如图1,为保护河上古桥OA,规划建一座新桥BC,同时设立一个圆形保护区,规划要求,新桥BC与河岸AB垂直;保护区的边界为圆心M在线段OA上并与BC相切的圆,且古桥两端O和A到该圆上任一点的距离均不少于80 m,经测量,点A位于点O正北方向60 m处,点C位于点O正东方向170 m处,(OC为河岸),tan∠BCO=4/3. As shown in Figure 1, in order to protect the ancient bridge OA on the river, a new bridge BC is planned and a circular protection zone is set up. Planning requirements are as follows: New Bridge BC is perpendicular to the river bank AB; The boundary is the circle whose center M is tangent to BC in line segment OA, and the distance between O and A at any point on the circle at both ends of the ancient bridge is not less than 80 m. When measured, point A is located at the point O O At point m, point C is located 170 m to the east of point O (OC is bank) and tan ∠ BCO = 4/3.