7. 1 Line segment related to triangle

Triangles are stable.

7.2 Angle related to triangle

The sum of the internal angles of a triangle is equal to 180 degrees.

The outer angle of a triangle is equal to the sum of two non-adjacent inner angles.

The outer angle of a triangle is greater than any inner angle that is not adjacent to it.

7.3 sum of polygons and their internal angles

Is the sum of the internal angles of the N-polygon equal to: (n-2)? 180 degrees

The sum of the outer angles of a polygon is equal to 360 degrees.

Chapter VIII Binary Linear Equations

8. 1 binary linear equations

An equation contains two unknowns (X and Y) whose exponents are 1. Equations like this are called binary linear equations.

Two binary linear equations are combined to form a system of linear equations with two unknowns.

The values of two unknowns that make the values on both sides of the binary linear equation equal are called the solutions of the binary linear equation.

The common * * * solution of two equations of binary linear equations is called the solution of binary linear equations.

8.2 elimination

The idea of solving the unknowns one by one from more to less is called elimination thought.

Chapter 9 Inequality and Unequal Groups

9. 1 inequality

Formulas that indicate the size relationship with less than sign or greater than sign are called inequalities.

The value of the unknown quantity that makes the inequality valid is called the solution of the inequality.

The value range of x that can make inequality hold is called the solution set of inequality, which is called the solution set for short.

An inequality whose unknown number is 1 is called a linear inequality of one variable.

The essence of inequality:

Add (or subtract) the same number (or formula) on both sides of the inequality, and the direction of the inequality remains unchanged.

Both sides of inequality multiply (or divide) the same positive number, and the direction of inequality remains unchanged.

When both sides of the inequality are multiplied (or divided) by the same negative number, the direction of the inequality changes.

The difference between any two sides in a triangle is less than the third side.

The sum of any two sides in a triangle is greater than the third side.

9.3 One-dimensional linear inequality system

When two linear inequalities are combined, a unitary linear inequality is formed.

Chapter 10 Real Numbers

10. 1 square root

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, and 2 is the root index.

The arithmetic square root of A is pronounced as "root number A", and A is called radix.

The arithmetic square root of 0 is 0.

If the square of a number is equal to a, then this number is called the square root or quadratic root of a.

The operation of finding the square root of a number is called square root.

10.2 cube root

If the cube of a number is equal to A, then this number is called the cube root or cube root of A. ..

The operation of finding the cube root of a number is called finding the cube root.

10.3 real number

Infinitely cyclic decimals are also called irrational numbers.

Rational numbers and irrational numbers are collectively called real numbers.