There are many knowledge points in junior high school mathematics. If you want to learn junior high school mathematics well, you must establish a systematic knowledge framework. In this article, I will sort out the important knowledge points of junior high school mathematics for your reference. The theorem of the basic theorem of junior middle school mathematics (1): 1. There is only one straight line after two points. 2. The line segment between two points is the shortest. (2) Angle theorem: 1. The complementary angles of the same angle or the same angle are equal. 2. The complementary angles of the same angle or equal angle are equal. (3) Straight line theorem: 1. One and only one straight line is perpendicular to the known straight line. 2. Of all the line segments connecting a point outside the straight line with points on the straight line, the vertical line segment is the shortest. (4) parallelism theorem 1. Congruent angles are equal and two straight lines are parallel; Internal dislocation angles are equal and two straight lines are parallel; The internal angles on the same side are complementary and the two straight lines are parallel. 2. The same angle is equal and two straight lines are parallel; Internal dislocation angles are equal and two straight lines are parallel; The internal angles on the same side are complementary and the two straight lines are parallel. (4) congruent triangles's judgment (1)SSS (side by side): the triangle with three sides corresponding to the same is congruent triangles. (2)SAS (Angle and Edge): A triangle with two edges and their included angles equal to each other is congruent triangles. (3)ASA (Angle and Angle): the congruence of two angles and their corresponding equal triangles. (4)AAS (corner edge): two corners and the opposite side of one corner correspond to equal triangular congruences. (5)RHS (right angle, hypotenuse and edge): In a pair of right-angled triangles, the hypotenuse is equal to the other right-angled edge. (5) parallelogram judgment theorem 1. Two sets of quadrangles with equal diagonals are parallelograms. 2. Two groups of quadrilaterals with equal opposite sides are parallelograms. 3. Quadrilaterals whose diagonals are bisected with each other are parallelograms. 4. A set of quadrilaterals with parallel and equal opposite sides is a parallelogram. Related knowledge points of a circle (1) A closed curve formed by taking a moving point as the center and a certain length as the distance on a plane is called a circle. A circle has countless axes of symmetry. (2) Related characteristics of cycles 1. The line segment connecting the center of the circle and any point on the circle is called radius, the letter is R, the line segment passing through the center of the circle on the circle is called diameter, the letter is D, and the straight line with diameter is the symmetry axis of the circle. In the same circle, the diameter of the circle is d=2r. 2. A line segment connecting any two points on a circle is called a chord. The longest chord in the same circle is the diameter. The straight line with the diameter is the symmetry axis of the circle, so there are countless symmetry axes of the circle. 3. The part between any two points on an arc circle is called an arc, which is represented by "⌒". An arc larger than a semicircle is called an optimal arc, and an arc smaller than a semicircle is called a suboptimal arc, so a semicircle is neither an optimal arc nor a suboptimal arc. The optimal arc is generally represented by three letters, and the suboptimal arc is generally represented by two letters. The optimal arc is an arc with a central angle greater than 180 degrees, and the suboptimal arc is an arc with a central angle less than 180 degrees. In the same circle or equal circle, two arcs that can overlap each other are called equal arcs. 4. The angle of the vertex on the center of the circle is called the central angle. The angle at which the vertex is on the circumference and both sides intersect with the circle is called the circumferential angle. The angle of a circle is equal to half the central angle of the same arc. One-dimensional linear equation (1) 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, so it is called one-dimensional linear equation. Finding the value of the unknown quantity in the equation is called the solution of the equation. One-dimensional linear equations are linear equations with only one root. (2) The condition for judging a linear equation (1) must be an equation first. (2) Secondly, it must contain an unknown number. (3) There are no unknowns in the denominator. (III) Root Formula Method For the unary linear equation ax+b=0(a≠0), the root formula is: X =-B/A. The derivation process AX+B = 0AX =-B/A. General method (1) Denominator: Denominator refers to (2 After removing the brackets and the "+"sign in front of them, the symbols of the items in the original brackets remain unchanged. Parentheses are preceded by "-". After removing the brackets and the "-"sign in front of them, the symbols of the original brackets will change. (Replace with the opposite symbol, for example: -(x-y)=-x+y). (3) Shifting terms: adding (or subtracting) the same number or the same algebraic expression on both sides of the equation is equivalent to changing the signs of some terms in the equation and moving them from one side of the equation to the other. This deformation is called a shift term. (4) Merging similar items Merging similar items is to add the coefficients of similar items by using the multiplication and distribution law, and the obtained results are taken as coefficients, and the letters and indexes remain unchanged. By merging similar terms, the one-dimensional linear equation is transformed into the simplest form: ax=b(a≠0) (5) the coefficient is transformed into 1. Let the equation become ax=b type (a≠ 1, a≠0) after constant deformation, then the process AX = B → X = This is the general step and the last step to solve the equation. That is, both sides of the equation are divided by the coefficient of the unknown term at the same time. Finally, we get the form of x = a.