To measure the diameter of a small hole on a steel plate, an indirect measurement method is usually used. If a standard steel ball with a diameter of 10 mm is placed on the small hole, the distance between the top of the steel ball and the plane of the small hole H = 8 & nbsp; mm (as shown in the figure), and the diameter D of the small hole is calculated

To measure the diameter of a small hole on a steel plate, an indirect measurement method is usually used. If a standard steel ball with a diameter of 10 mm is placed on the small hole, the distance between the top of the steel ball and the plane of the small hole H = 8 & nbsp; mm (as shown in the figure), and the diameter D of the small hole is calculated

Make OD ⊥ AB, intersection ⊙ O and point C, connect ob. According to the vertical diameter theorem, CD vertically bisects ab.. CD = H = 8mm, OD = cd-co = 3mm. In RT △ ODB, BD2 = ob2-od2 = 16, ⊥ BD = 4mm. ⊥ AB = 2bd = 8mm. A: the diameter D of the hole is 8mm