1, the perimeter of the rectangle = (length+width) ×2, and C=(a+b)×2.

2. The circumference of a square = side length ×4, and C=4a.

3. The area of a rectangle = length × width, and S=ab.

4. area of square = side length × side length, S = a 2.

5. The area of triangle = base × height ÷2, and S=ah÷2.

6. The area of parallelogram = base × height, and S=ah.

7. Trapezoidal area = (upper bottom+lower bottom) × height ÷2, S=(a+b)h÷2.

The significance of learning mathematics:

1. Enhance logical thinking and analytical ability: Mathematics is a discipline with strict logic. Learning mathematics can exercise our logical thinking and analytical ability and improve our problem-solving ability.

2. Cultivate abstract thinking and innovative thinking: There are many abstract concepts and ways of thinking in mathematics. Learning mathematics can cultivate our abstract thinking and innovative thinking, and make us more capable of discovery and creation.

3. Improve mathematical literacy and mathematical application ability: Mathematics is a subject widely used in various fields. Learning mathematics can improve our mathematical literacy and mathematical application ability, so as to better cope with practical problems and challenges.

4. Improve humanistic quality and cultural quality: Mathematics is a common knowledge form in the development of human civilization. Learning mathematics can improve our humanistic quality and cultural accomplishment and help us better understand and appreciate the essence of human civilization.