The good habits of learning the important knowledge of junior high school mathematics should be: asking more questions, thinking hard, doing easily, summarizing again and paying attention to application. This is an important knowledge point of junior high school mathematics that I sorted out. I hope you can learn something from it!

The first part number and algebra

I. Numbers and formulas:

1, rational number

Rational Numbers: ① Integer → Positive Integer /0/ Negative Integer

② Score → Positive/Negative Score

Number axis: ① Draw a horizontal straight line, take a point on the straight line to represent the origin of 0, select a certain length as the unit length, and specify the right direction on the straight line as the positive direction to get the number axis. ② Any rational number can be represented by a point on the number axis. (3) If two numbers differ only in sign, then we call one of them the inverse of the other number, and we also call these two numbers the inverse of each other. On the number axis, two points representing the opposite number are located on both sides of the origin, and the distance from the origin is equal. The number represented by two points on the number axis is always larger on the right than on the left. Positive numbers are greater than 0, negative numbers are less than 0, and positive numbers are greater than negative numbers.

Absolute value: ① On the number axis, the distance between the point corresponding to a number and the origin is called the absolute value of the number. (2) The absolute value of a positive number is itself, the absolute value of a negative number is its reciprocal, and the absolute value of 0 is 0. Comparing the sizes of two negative numbers, the absolute value is larger but smaller.

Operation of rational number:

Addition: ① Add the same sign, take the same sign, and add the absolute values. ② When the absolute values are equal, the sum of different symbols is 0; When the absolute values are not equal, take the sign of the number with the larger absolute value and subtract the smaller absolute value from the larger absolute value. (3) A number and 0 add up unchanged.

Subtraction: Subtracting a number equals adding the reciprocal of this number.

Multiplication: ① Multiplication of two numbers, positive sign of the same sign, negative sign of different sign, absolute value. ② Multiply any number by 0 to get 0. ③ Two rational numbers whose product is 1 are reciprocal.

Division: ① Dividing by a number equals multiplying the reciprocal of a number. ②0 is not divisible.

Power: the operation of finding the product of n identical factors A is called power, the result of power is called power, A is called base, and N is called degree.

Mixing order: multiply first, then multiply and divide, and finally add and subtract. If there are brackets, calculate first.

2. Real numbers

Irrational number: Infinitely circulating decimals are called irrational numbers.

Square root: ① If the square of a positive number X is equal to A, then this positive number X is called the arithmetic square root of A. If the square of a number X is equal to A, then this number X is called the square root of A. (3) A positive number has two square roots /0 square root is 0/ negative number without square root. (4) Find the square root of a number, which is called the square root, where a is called the square root.

Cubic root: ① If the cube of a number X is equal to A, then this number X is called the cube root of A. ② The cube root of a positive number is positive, the cube root of 0 is 0, and the cube root of a negative number is negative. The operation of finding the cube root of a number is called square root, where a is called square root.

Real numbers: ① Real numbers are divided into rational numbers and irrational numbers. ② In the real number range, the meanings of reciprocal, reciprocal and absolute value are exactly the same as those of reciprocal, reciprocal and absolute value in the rational number range. ③ Every real number can be represented by a point on the number axis.

3. Algebraic expressions

Algebraic expression: A single number or letter is also an algebraic expression.

Merge similar items: ① Items with the same letters and the same letter index are called similar items. (2) Merging similar items into one item is called merging similar items. (3) When merging similar items, we add up the coefficients of similar items, and the indexes of letters and letters remain unchanged.

4. Algebraic expressions and fractions.

Algebraic expression: ① The algebraic expression of the product of numbers and letters is called monomial, the sum of several monomials is called polynomial, and monomials and polynomials are collectively called algebraic expressions. ② In a single item, the index sum of all letters is called the number of times of the item. ③ In a polynomial, the degree of the term with the highest degree is called the degree of this polynomial.

Algebraic expression operation: when adding and subtracting, if you encounter brackets, remove them first, and then merge similar items.

Power supply operation: AM+AN=AM+N

AMN=AMN

A/BN = a/BN division.

Multiplication of algebraic expressions: ① Multiply the monomial with the monomial, respectively multiply their coefficients and the power of the same letter, and the remaining letters, together with their exponents, remain unchanged as the factors of the product. (2) Multiplying polynomial by monomial means multiplying each term of polynomial by monomial according to the distribution law, and then adding the products. (3) Polynomial multiplied by polynomial. Multiply each term of one polynomial by each term of another polynomial, and then add the products.

There are two formulas: square difference formula/complete square formula.

Algebraic division: ① monomial division, which divides the coefficient and the power of the same base as the factor of quotient respectively; For the letter only contained in the division formula, it is used as the factor of quotient together with its index. (2) Polynomial divided by single item, first divide each item of this polynomial by single item, and then add the obtained quotients.

Factorization: transforming a polynomial into the product of several algebraic expressions. This change is called factorization of this polynomial.

Methods: Common factor method, formula method, grouping decomposition method and cross multiplication were used.

Fraction: ① Algebraic expression A is divided by algebraic expression B. If the divisor B contains a denominator, then this is a fraction. For any fraction, the denominator is not 0. ② The numerator and denominator of the fraction are multiplied or divided by the same algebraic expression that is not equal to 0, and the value of the fraction remains unchanged.

Operation of fraction:

Multiplication: take the product of molecular multiplication as the numerator of the product, and the product of denominator multiplication as the denominator of the product.

Division: dividing by a fraction is equal to multiplying the reciprocal of this fraction.

Addition and subtraction: ① Addition and subtraction with denominator fraction, denominator unchanged, numerator addition and subtraction. ② Fractions with different denominators shall be divided into fractions with the same denominator first, and then added and subtracted.

Fractional equation: ① The equation with unknown number in denominator is called fractional equation. ② The solution whose denominator is 0 is called the root increase of the original equation.

Equations and inequalities

1, equation and equation

Unary linear equation: ① In an equation, there is only one unknown, and the exponent of the unknown is 1. Such an equation is called a one-dimensional linear equation. ② Adding or subtracting or multiplying or dividing an algebraic expression that is not 0 on both sides of the equation at the same time, the result is still an equation.

Steps to solve a linear equation with one variable: remove the denominator, shift the term, merge the similar terms, and change the unknown coefficient into 1.

Binary linear equation: An equation that contains two unknowns and whose terms are 1 is called binary linear equation.

Binary linear equations: The equations composed of two binary linear equations are called binary linear equations.

A set of unknown values suitable for binary linear equation is called the solution of this binary linear equation.

The common * * * solution of each equation in a binary linear system of equations is called the solution of this binary linear system of equations.

Methods of solving binary linear equations: substitution elimination method/addition and subtraction elimination method.

Quadratic equation of one variable: an equation with only one unknown and the highest coefficient of the unknown term is 2.

The relationship between quadratic functions of 1 unary quadratic equation

Everyone has studied quadratic function, that is, parabola, and has a deep understanding of it, such as solution, representation in images and so on. In fact, the quadratic equation of one variable can also be expressed by quadratic function. In fact, the quadratic equation of one variable is also a special case of quadratic function, that is, when y is 0, it constitutes the quadratic equation of one variable. Then if expressed in the plane rectangular coordinate system, the quadratic equation of one variable is the intersection of the image and the X axis in the quadratic function. Which is the solution of the equation.

2 the solution of quadratic equation in one variable

As we all know, quadratic function has vertices -b/2a, 4ac-b2/4a, which is a very important point to remember, because as mentioned above, the quadratic equation of one variable is also a part of quadratic function, so he also has his own solution, with which he can find all the solutions of the quadratic equation of one variable.

1 collocation method

Using this formula, the equation is transformed into a complete square formula and solved by direct Kaiping method.

2-factor decomposition method

Select the common factor, apply the formula, and cross multiply. The same is true for solving quadratic equations with one variable. Using this, the equation can be solved in the form of several products.

3 formula method

This method can also be used as a general method to solve quadratic equations with one variable. The roots of the equation are X 1={-b+√[b2-4ac]}/2a, and X2={-b-√[b2-4ac]}/2a.

Three steps to solve quadratic equation:

1 Steps of matching method:

First, the constant term is moved to the right of the equation, then the coefficient of the quadratic term is changed to 1, and the square of half the coefficient of 1 is added, and finally the complete square formula is obtained.

Two steps of factorization:

Turn the right side of the equation to 0, and then see if you can extract the common factor. The formula method here refers to the formula method or cross multiplication in factorization, which can be changed into product form if possible.

3 formula method

Simply substitute the coefficient of quadratic equation into a variable, where the coefficient of quadratic term is a, the coefficient of linear term is b, and the coefficient of constant term is c.

4 Vieta Theorem

Understand with Vieta theorem, Vieta theorem in a quadratic equation, the sum of two roots =-b/a, the product of two roots = c/a.

It can also be expressed as x 1+x2 =-b/a, and x1x2 = c/a. By using Vieta's theorem, we can find out the coefficients in a quadratic equation with one variable, which is very common in the topic.

5 The case of the root of a linear equation with one variable

Using the discriminant of roots to understand, the discriminant of roots can be written as "Delta" and read as "Tune ta", and Delta = B2-4ac can be divided into three situations:

I am △ > 0, a quadratic equation with one variable has two unequal real roots;

II When △=0, the quadratic equation of one variable has two identical real roots;

Three dang △

2. Inequality and unequal groups

Inequality: ① The formula connecting ÷ = ÷ with the symbol is called inequality. ② Add or subtract the same algebraic expression on both sides of the inequality, and the direction of the inequality remains unchanged. ③ Both sides of inequality are multiplied or divided by a positive number, and the direction of inequality remains unchanged. ④ Both sides of inequality are multiplied or divided by the same negative number, and the unequal numbers are in opposite directions.

Solution set of inequality: ① The value of unknown quantity that can make inequality hold is called the solution of inequality. (2) All solutions of an inequality with unknowns constitute the solution set of this inequality. ③ The process of finding the solution set of inequality is called solving inequality.

Unary linear inequality: An inequality with algebraic expressions on both sides and only one unknown with the highest degree of 1 is called unary linear inequality.

One-dimensional linear inequality group: ① Several one-dimensional linear inequalities about the same unknown quantity are combined into one-dimensional linear inequality group. ② The common part of the solution set of each inequality in a linear inequality group is called the solution set of this linear inequality group. ③ The process of finding the solution set of inequality group is called solving inequality group.

Symbolic direction of one-dimensional linear inequality;

In one-dimensional linear inequality, unlike equality, the equal sign is a constant, which changes with your addition or multiplication.

In inequality, if the same number or positive number is added, the sign of inequality will not change direction; For example: A>b, A+C > B+C

In inequality, if you subtract the same number or add a negative number, the sign of inequality will not change direction; For example: A>b, A-C > B-C

In inequality, if multiplied by the same positive number, the unequal numbers do not change direction; For example: A>b, A * C > B * CC & gt0

In inequality, if multiplied by the same negative number, the sign of inequality changes direction; For example: A>b, A * C<B * CC<0.

If the inequality is multiplied by 0, the inequality becomes an equal sign.

Therefore, the number of multiplications is required in the topic, so it depends on whether there is one-dimensional inequality in the topic. If there is, then the number multiplied by the inequality is not equal to 0, otherwise the inequality is not established;

3. Function

Variable: dependent variable, independent variable.

When images are used to represent the relationship between variables, points on the horizontal axis are usually used as independent variables, and points on the vertical axis are used to represent dependent variables.

Linear function: ① If the relationship between two variables X and Y can be expressed in the form that Y=KX+BB is constant and K is not equal to 0, then Y is said to be a linear function of X. ② When B=0, Y is said to be a proportional function of X. ..

Image of linear function: ① Take the values of independent variable X and corresponding dependent variable Y of a function as the abscissa and ordinate of points respectively, and draw the corresponding points in rectangular coordinate system. A graph composed of all these points is called an image of a function. ② The image with the proportional function Y=KX is a straight line passing through the origin. ③ In the linear function, when k < 0 and b < 0, it passes through 234 quadrants; When k < 0, b > 0, pass through quadrant124; When k > 0 and b < 0, pass through quadrant134; When k > 0 and b > 0, pass through quadrant 123. ④ When k > 0, y value increases with the increase of x value, and when x < 0, y value decreases with the increase of x value.

Part II Space and Graphics

First, the understanding of graphics

1, point, line, surface

Points, lines and surfaces: ① A figure consists of points, lines and surfaces. (2) Lines intersecting face to face and points where lines intersect. (3) Points become lines, lines become surfaces, and surfaces become bodies.

Unfolding and folding: ① In a prism, the intersection of any two adjacent faces is called an edge, and the side edge is the intersection of two adjacent edges. All sides of the prism are equal in length, the upper and lower bottom surfaces of the prism are the same in shape, and the side surfaces are cuboids. (2) N prism is a prism with N faces on its bottom.

Cutting a geometric figure: cutting a figure with a plane, and the cutting surface is called a section.

Views: main view, left view and top view.

Polygon: It is a closed figure composed of some line segments that are not on the same straight line.

Arc and sector: ① A figure consisting of an arc and two radii passing through the end of the arc is called a sector. ② The circle can be divided into several sectors.

2. Angle

Line: ① A line segment has two endpoints. (2) The line segment extends infinitely in one direction to form a ray. A ray has only one endpoint. ③ A straight line is formed by the infinite extension of both ends of a line segment. A straight line has no end. Only one straight line passes through two points.

Comparison length: ① Of all the connecting lines between two points, the line segment is the shortest. ② The length of the line segment between two points is called the distance between these two points.

Measurement and expression of angle: ① An angle consists of two rays with a common endpoint, and the common endpoint of the two rays is the vertex of the angle. ② One degree of 1/60 is one minute, and one minute of1/60 is one second.

Comparison of angles: ① An angle can also be regarded as a light rotating around its endpoint. (2) The ray rotates around its endpoint. When the ending edge and the starting edge are on a straight line, the angle formed is called a right angle. The starting edge continues to rotate, and when it coincides with the starting edge again, the angle formed is called fillet. (3) The ray from the vertex of an angle divides the angle into two equal angles, and this ray is called the bisector of the angle.

Parallelism: ① Two straight lines that do not intersect in the same plane are called parallel lines. ② One and only one straight line is parallel to this straight line after passing through a point outside the straight line. If both lines are parallel to the third line, then the two lines are parallel to each other.

Perpendicular: ① If two lines intersect at right angles, they are perpendicular to each other. (2) The intersection of two mutually perpendicular straight lines is called vertical foot. ③ On the plane, there is one and only one straight line perpendicular to the known straight line at one point.

Perpendicular bisector: A straight line perpendicular to and bisecting a line segment is called perpendicular bisector.

The perpendicular bisector in perpendicular bisector must be a line segment, not a ray or a straight line, which is related to the infinite extension of rays and straight lines. Looking back, the middle vertical line is a straight line, so when drawing the middle vertical line, we will determine the drawing method after 2 o'clock, and later we will talk about the need to cross the line segment at 2 o'clock.

Perpendicular bisector theorem;

Property theorem: the distance between the point on the middle vertical line and the two ends of the line segment is equal;

Decision Theorem: The point with the same distance from the endpoint of line segment 2 is on the middle vertical line of this line segment.

Angular bisector: The ray bisecting an angle is called the angular bisector of the angle.

There are several points to note in the definition, that is, the bisector of an angle is a ray, not a line segment or a straight line. Many times there will be a straight line in the topic, which is the symmetry axis of the bisector, which also involves the problem of trajectory. The bisector of an angle is a point with equal distance to both sides of the angle.

Property theorem: the distance between the point on the bisector of an angle and both sides of the angle is equal.

Decision theorem: the points with equal distance to both sides of the angle are on the bisector of the angle.

Square: A set of rectangles with equal adjacent sides is a square.

Properties: Square has all the properties of parallelogram, rhombus and rectangle.

Judgment: 1, rhombus 2 with equal diagonals and rectangle with equal adjacent sides.

& gt& gt& gt More exciting on the next page.