Rectangular area = length × width, S=ab

Square area = side length × side length, s = a.

Triangle area = base × height ÷2

2. Linear function formula

The linear function is a straight line, and the expression is as follows.

Point oblique type: y-b = k (x-a); The slope k and the intersection (a, b) are known.

Two-point formula: (y-b)/(x-a)=(b-d)/(a-c)

3. Quadratic function formula

Quadratic function is a parabola, and there are three expressions.

General formula: y=ax? +bx+c； (a≠0)

Vertex: y=a(x-h)? +k； [a≠0 fixed point (h, k)]

4. formulas of trigonometric functions

sin(A+B)= Sina cosb+cosa sinb sin(A-B)= Sina cosb-sinb cosa

cos(A+B)= cosa cosb-Sina sinb cos(A-B)= cosa cosb+Sina sinb

Learning rules

Mathematical concept is the cornerstone of junior high school mathematics, and it is the carrier of mathematical thinking mode and method. Many students encounter difficulties in solving math problems. Tracing back to the source, they often find that they have a problem with a certain mathematical concept, which prevents them from solving the problem.

Concept belongs to rational knowledge, and its formation depends on perceptual knowledge. The psychological characteristics of students are easy to understand and accept specific perceptual knowledge. Learning methods of mathematical concepts: In the learning process, we should understand the occurrence and formation of concepts, clarify the differences and connections between concepts, and form a network of related concepts in our minds to achieve a comprehensive and flexible application.