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

2, the perimeter of the square = side length × 4 = 4a;

3. The circumference of a circle = pi × diameter = π d = pi × radius× 2 = 2π r.

Second, the area formula

1, rectangular area = length× width S = ab；;

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

3. The area of triangle = base × height ÷ 2s = ah ÷ 2;

4. area of parallelogram = base × height S = ah

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

Thirdly, multiplicative commutative law.

Multiplicative commutative law is a calculation rule. When two numbers are multiplied, the position of the exchange factor remains the same. Their product is called multiplication exchange law, and a×b=bxa is represented by letters.

Generally, in the formula calculation with only multiplication, the calculation is usually done in the order from left to right. Sometimes, the law of multiplication and exchange can be used to perform simple operations.

Fourthly, one-dimensional linear equation.

One-dimensional linear equation refers to an equation with only one unknown number, the highest order of which is 1, and both sides are algebraic expressions. A linear equation with one variable has only one root.

One-dimensional linear equation can solve most engineering problems, travel problems, distribution problems, profit and loss problem, integral table problems, telephone billing problems and digital problems.

Five, the law of multiplication and distribution

Multiplication and distribution law refers to the sum of two numbers multiplied by one number. You can multiply them by this number first, and then add up the products.

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