Simplifying Algebraic Expressions (KS3 Cambridge p28.2) | 化简代数表达式（KS3剑桥 p28.2）

📚 Simplifying Algebraic Expressions (KS3 Cambridge p28.2) | 化简代数表达式（KS3剑桥 p28.2）

Algebra is often described as the language of mathematics, and simplifying expressions is one of the first essential grammar rules you need to master. In the Cambridge KS3 curriculum, the skills covered in p28.2 help you move from recognising variables to confidently collecting like terms, expanding brackets and substituting values. This article breaks down each idea into clear steps, common mistakes, and exam-style checks so you can build a strong algebraic foundation.

代数常被称为数学的语言，而化简表达式是你必须掌握的第一批核心语法规则之一。在剑桥 KS3 课程中，p28.2 所涉及的技能帮助你从认识变量开始，逐步学会合并同类项、展开括号和代入求值。本文把每个知识点拆成清晰的步骤、常见错误和考试式检查，帮助你打下扎实的代数基础。

1. What Are Algebraic Expressions? | 什么是代数表达式？

An algebraic expression is a combination of numbers, variables and operation signs such as +, −, × and ÷. Unlike an equation, an expression does not contain an equals sign. For example, 3x + 5, 2a − 7b and 4n² + 3n − 1 are all expressions. In KS3, you learn to simplify these expressions so they become shorter and easier to work with.

代数表达式是由数字、变量和 +、−、×、÷ 等运算符号组成的式子。与方程不同，表达式不包含等号。例如 3x + 5、2a − 7b 和 4n² + 3n − 1 都是表达式。在 KS3 阶段，你要学会化简这些表达式，使它们更简短、更容易处理。

Think of an expression as a phrase: 3x + 5 says “three lots of a number plus five”. There is no assertion that it equals anything, so you cannot ‘solve’ it in the usual sense. You can only rewrite it in a simpler equivalent form.

可以把表达式看成一个短语：3x + 5 的意思是 “一个数的三倍再加五”。它没有声称等于什么，所以你不能像解方程那样去 “解” 它。你只能把它改写成更简洁的等价形式。

2. Key Words: Term, Coefficient and Variable | 核心词汇：项、系数和变量

A term is a single number, a single variable, or numbers and variables multiplied together. In the expression 5x + 3y − 7, the terms are 5x, 3y and −7. The number part in a term is called the coefficient. So in 5x, the coefficient is 5; in 3y, the coefficient is 3; and for a constant term like −7, the number itself is the term.

项是一个单独的数、一个

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