Two men are walking in the park. One is Mr Brown , a worker, the other is Mr Black. Mr Brown is going to a chair. It is by the road. Mr Black is after him. Mr Brown finds Mr Black. Now Mr Black begins to walk faster(更快). Because he wants to get to the chair before Mr Black. Now Mr Black begins to walk faster because he also wants to get to the chair first. Then they both run .Mr Black runs faster than (比) Mr Brown. So he gets to the chair first and sits down on it. Mr Brown runs after Mr Black. When he gets to the chair. He sees Mr Black sitting on it. He is sorry to show a notice(通知)with the words“Wet Paint(油漆未干)”to Mr Black . Now Mr Black knows why Mr Brown is going to the chair.
的根在区间
上，则
的值为