Two-stage operation, first multiply and then divide, then add and subtract.

Circumference:

The circumference of a rectangle = (length+width) ×2 = 2(a+b) = (a+b)×2.

The circumference of a square = side length ×4 = 4a.

Circumference = pi× diameter = π d = pi× radius× 2 = 2π r.

Region:

Area of rectangle = length× width S = ab.

Area of a square = side length × side length S = a? .

Area of triangle = base × height ÷2 S=ah÷2.

Area of parallelogram = base × height S=ah.

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

Diameter = radius× 2d = 2r.

Radius = diameter ÷2 r=d÷2.

Area of circle = π× radius× radius.

Extended data:

Among the four operations, addition and subtraction are called primary operations, and multiplication and division are called secondary operations. Expressions that contain two or more operations are usually called mixed operations. The mixed operation of addition, subtraction, multiplication and division is also called elementary arithmetic. In elementary arithmetic, the prescribed calculation order is called operation order. Mathematically speaking, the order of these four operations is as follows:

(1) sibling operations In an expression, if only sibling operations are included, the operations should be performed from left to right. That is to say, only addition and subtraction, or only multiplication and division are mixed operations, and their operation order is calculated from left to right.

(2) Primary to secondary operations:

In an expression, if both first-level operation and second-level operation are included, then the second-level operation should be calculated first, and then the first-level operation should be calculated. That is, "multiply first and then divide, then add and subtract", or "multiply first and then divide, then add and subtract" for short.

Baidu encyclopedia-elementary arithmetic