📚 Simplifying Algebraic Expressions (Cambridge KS3 p113) | 化简代数表达式（剑桥KS3数学第113页）
Welcome to this revision guide based on page 113 of the Cambridge KS3 Mathematics textbook. Here we explore the fundamentals of algebraic expressions, learning how to simplify them by combining like terms, using the distributive law, and substituting values. Mastering these skills is crucial for your success in algebra.
欢迎来到这篇基于剑桥KS3数学教材第113页的复习指南。我们将探索代数表达式的基础知识，学习如何通过合并同类项、运用分配律和代入数值来化简表达式。掌握这些技能对你的代数学习至关重要。
1. What is an Algebraic Expression? | 什么是代数表达式？
An algebraic expression is a combination of numbers, variables (letters representing unknown values), and operation symbols (+, −, ×, ÷). For example, 3x + 2, 5a − 7b, and x² + 2x − 4 are all algebraic expressions. Unlike an equation, an expression does not contain an equals sign. Think of it as a phrase in mathematics that describes a quantity.
代数表达式是由数字、变量（代表未知值的字母）和运算符号（+、−、×、÷）组合而成的。例如，3x + 2、5a − 7b 和 x² + 2x − 4 都是代数表达式。与方程不同，表达式不包含等号。可以把它看作是数学中描述数量的短语。
3x + 2y − 5
2. Understanding Terms, Coefficients, and Constants | 理解项、系数和常数
Every algebraic expression is made up of terms. A term can be a single number, a variable, or a number multiplied by a variable. For instance, in 4x² + 3x − 7, the terms are 4x², 3x, and −7. The number in front of a variable is called the coefficient (e.g., 4 is the coefficient of x², 3 is the coefficient of x). A term without a variable is a constant (here, −7).
每个代数表达式都由项组成。项可以是单个数字、变量或数字与变量的乘积。例如，在 4x² + 3x − 7 中，项为 4x²、3x 和 −7。变量前面的数字称为系数（例如，4 是 x² 的系数，3 是 x 的系数）。没有变量的项是常数（此处为 −7）。
3. Like Terms and Unlike Terms | 同类项与异类项
Like terms are terms that have exactly the same variable part, including the same power. For example, 2x and 5x are like terms because both contain x to the power of 1. Similarly, 3y² and −y² are like terms. Unlike terms have different variable parts: 2x and 3x² are not like terms, and 4a and 5b are also not like terms. Only like terms can be combined through addition or subtraction.
同类项是指变量部分完全相同（包括相同的指数）的项。例如，2x 和 5x 是同类项，因为两者都含有 x 的一次方。同样，3y² 和 −y² 也是同类项。异类项的变量部分不同：2x 和 3x² 不是同类项，4a 和 5b 也不是同类项。只有同类项才能通过加法或减法合并。
4. Simplifying Expressions by Collecting Like Terms | 通过合并同类项化简
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