Counting is a common question in primary school mathematics examination. If you don't master the right skills, it's easy to make mistakes. Today, I'm going to teach you how to count numbers, without repetition or omission.

First, calculate the number of line segments.

Mark 1, 2, 3 ... in turn, every two points are n, and then add all the marked numbers, that is, the number of all line segments, with 1+2+3+4+...+(n- 1) line segments.

Second, count the number of angles

Every two adjacent rays are marked with 1, 2, 3 ... in turn, and then all the marked numbers are added up, which is the number of all angles, so there are 1+2+3+4+...+(n- 1) angles.

Third, count the number of rectangles.

The following formula can be used to count rectangles: the total number of long sides × the total number of short sides = the number of rectangles.

Fourth, count the number of squares.

The number of squares in a square composed of the same n×n small squares is:/kloc-0 /×1+2× 2+…+n× n.

In fact, in the stage of laying the foundation in primary school, the first thing children should think of is drawing charts and tabulating to solve all problems. It is necessary to form such a habit. This kind of consciousness can be formed when they are in senior grade, and graphics and tables can emerge in their minds, which is very helpful and efficient for solving problems in the future.