Second, the integer mixed operation, the operation order is easy to make mistakes.

Third, the multiplication formula is not skilled.

Fourth, understand the angle: the size of the angle has nothing to do with the length of the side, but with the size of the mouth on both sides.

5. Time, minutes, seconds, unit conversion is easy to make mistakes.

Six, measuring length, ruler is not standardized, reading scale is not accurate, unit conversion is easy to make mistakes.