钟面角是指时钟的时针与分针所成的角．如图，图①、图②、图③三个钟面上的时刻分别记录了某中学的早晨上课时间7：30、中午放学时间11：50、下午放学时间17：00．

Question

钟面角是指时钟的时针与分针所成的角．如图，图①、图②、图③三个钟面上的时刻分别记录了某中学的早晨上课时间7：30、中午放学时间11：50、下午放学时间17：00．

（1）分别写出图中钟面角的度数：∠1＝       °、∠2＝       °、∠3＝       °；

（2）在某个整点，钟面角可能会等于90°，写出可能的一个时刻为       ；

（3）请运用一元一次方程的知识解决问题：钟面上，在7:30～8:00之间，钟面角等于90°的时刻是多少？

Answer 1

（1）45，55，150；············································································································· 3分

（2）如：3点；（答案不唯一）···························································································· 4分

（3）设从7：30开始，经过x分钟，钟面角等于90°．

根据题意，得6x－0.5x－45＝90．················································································· 6分

解得 ．············································································································· 7分

答：钟面上，在7:30～8:00之间，钟面角等于90°的时刻是7：54．·························· 8分