1， 1mm = 0. 1cm。

2. The method of rewriting the continuous addition formula into the multiplication formula. Find the sum of several identical addends, which can be calculated by multiplication.

3. subtraction without abdication: subtraction without borrowing high positions. For example: 56-22=34. You can subtract 2 from 6, so you don't have to borrow the first 5.

4. The size of the angle is related to the size of both sides, and has nothing to do with the length of both sides.

5. The acute angle is less than the right angle, and the obtuse angle is greater than the right angle.