Xiao Ming starts to do his homework at 9 o'clock. At the beginning, the hour hand and the minute hand end in the same line. When the hour hand and the minute hand overlap, how much time does Xiao Ming do his homework?

Xiao Ming starts to do his homework at 9 o'clock. At the beginning, the hour hand and the minute hand end in the same line. When the hour hand and the minute hand overlap, how much time does Xiao Ming do his homework?

At 9:00, the hour hand and the minute hand are in the same straight line. Set the minute hand on the X minute. The minute hand moves 6 degrees per minute. The angle between the minute hand and 12 is 6x degrees. The hour hand moves 30 degrees per hour and 1 / 2 degree per minute. At this time, it moves 1 / 2x degrees from 9:00. The angle between the hour hand and the minute hand is 90-1 / 2x degrees. Because the hour hand and the minute hand are in the same straight line, 90-1 / 2x + 6x = 180, x = 1

Why do you have so much homework? I have to stay up late today
If the teacher leaves too much homework, he won't have time to review, will he? Isn't that counterproductive? Why does the teacher leave so much homework?

The main reason why teachers leave too much homework is that they are afraid that they will forget what they have learned in class without digesting it. They are also afraid that you will just go home to play and forget to study, review and preview. You have to understand the teacher. If there is too much homework, you can also suggest to the teacher in the form of letters. If the teacher is reasonable (there is basically no impersonality), it will be reduced

Beijing Education Press, Beijing Publishing Group. With compulsory education curriculum standard experimental textbooks. I am a student of Fengming in Jincheng, Shanxi Province.