In △ABC, ∠ A+∠ C+2 ∠ 1+2 ∠ 2 = 360.

That is,180-∠ 3+2 ∠1+2 ∠ 2 = 360.

∴∠b'=90-0.5∠3 & lt； 90

In the same way, we can know: ∠ a'

∴ is an acute triangle.

There is generally no good way to solve this problem, but it depends on the usual experience. Obviously, the lowest score is-10 and the highest score is 50, so n must be less than 5 1 (from-10 to 50 * * 5 1).

Because answering a question correctly is 4 points, the score fluctuates the most. As the main line, if you only count one right question, it should be a multiple of 4, and the middle number is made up of what you did wrong and what you didn't do. So the more questions you do correctly, the less likely it is to form a continuous score, so start with the highest score of 40: when 40 is all right, the highest score is 36 (the other one didn't do it).

When you do eight questions correctly, the highest is 32 (the other two questions are not done), followed by 3 1 (one is wrong and the other is not done), 30 (both are wrong), 33 and 34 are not done, and so on, there is no 29, so you have to remove 45 from 5 1.

3. A day should be 24 hours. In fact, according to my understanding, it is to ask how many times the hour hand and the minute hand overlap in a day. If you start with 12, the next coincidence will exceed 1 and the next one will exceed 2: 00 ... until you go back to 12 again (not counting this time), so here it is at 65438+.

(For reference only)