1, perimeter of rectangle = (length+width) x2C=(a+b)x2, perimeter of square = side length x4C=4a, area of rectangle = length x width S=ab, area of square = side length x side length S=aa=a, area of triangle = bottom x height: 2S=ah2.
2. Pi is the ratio of the circumference to the diameter of a circle, which is generally expressed by the Greek letter π and is a common mathematical constant in mathematics and physics. π is also equal to the ratio of the square of the area and radius of a circle, which is the key value to accurately calculate the geometric shapes such as the circumference of a circle, the area of a circle and the volume of a ball. In the analysis, π can be strictly defined as the smallest positive number x satisfying sinx=0.
3. pi with the Greek letter π (pronounced [pa? ]), which is a constant (approximately equal to 3. 14 1592654), is the ratio of circumference to diameter. It is an irrational number, that is, an infinite cycle decimal. In daily life, pi is usually expressed as 3. 14, which is used for approximate calculation. 3. The nine decimal places of141592654 are enough for general calculation.