📚 G-2 Workbook 200: IGCSE Mathematics Core Practice | G-2 练习册 200：IGCSE 数学核心练习
This article supports G-2 Workbook 200, a 200-question IGCSE Mathematics practice set designed to build fluency in algebra, functions, geometry, ratio and probability. The worked explanations below show the exact methods examiners expect for core-level answers.
本文配套 G-2 练习册 200，这是一套包含 200 道题的 IGCSE 数学核心练习，旨在提高代数、函数、几何、比和概率的熟练度。下面的解析展示了核心层次答案中考官期望的标准方法。
1. Understanding the Practice Set Structure | 理解练习结构
Workbook 200 is split into four blocks of fifty questions, each mixing topics so that you practise switching between skills under timed conditions.
练习册 200 分为四个 50 题模块，每个模块混合多个主题，让你在计时条件下练习在不同技能之间切换。
Before attempting a block, scan the command words such as solve, factorise, evaluate, describe and justify, because these words tell you how much working is required.
开始一个模块前，先浏览题目中的指令词，例如 solve、factorise、evaluate、describe 和 justify，因为这些词会提示你需要写出多少步骤。
Mark each block with the official mark scheme, and record errors by topic rather than by question number.
使用官方评分标准和答案批改每个模块，并按主题而不是按题号记录错误。
2. Expanding and Factorising | 展开与因式分解
When expanding two brackets, multiply every term in the first bracket by every term in the second bracket, then collect like terms.
展开两个括号时，把第一个括号中的每一项分别乘以第二个括号中的每一项，然后合并同类项。
² − 6x. Second, (x + 1)(x − 4) = x² − 4x + x − 4 = x² − 3x − 4. Adding gives 3x² − 9x − 4.
示例：展开 2x(x − 3) + (x + 1)(x − 4)。先算 2x(x − 3) = 2x² − 6x，再算 (x + 1)(x − 4) = x² − 4x + x − 4 = x² − 3x − 4，最后相加得到 3x² − 9x − 4。
duct is 6 and whose sum is −5. The numbers are −2 and −3, so x² − 5x + 6 = (x − 2)(x − 3).
因式分解 x² − 5x + 6 时，要找两个数，它们的乘积是 6，和是 −5。这两个数是 −2 和 −3，因此 x² − 5x + 6 = (x − 2)(x − 3)。
3. Linear Equations and Rearranging | 线性方程与变形
For a linear equation, remove brackets first, collect x-terms on one side and constants on the other, then divide by the coefficient of x.
解线性方程时，先去括号，再把含 x 的项移到一边，常数移到另一边，最后除以 x 的系数。
x − 6 = 5x + 4. Subtract 3x from both sides: −6 = 2x + 4. Subtract 4: −10 = 2x, so x = −5.
解 3(x − 2) = 5x + 4：展开得 3x − 6 = 5x + 4。两边同时减 3x 得 −6 = 2x + 4；再减 4 得 −10 = 2x，所以 x = −5。
ng inverse operations. To make t the subject, subtract u and divide by a: t = (v − u) ÷ a.
变形公式如 v = u + at 时，用逆运算分离目标字母。要令 t 成为主项，先减 u 再除以 a：t = (v − u) ÷ a。
4. Quadratic Equations and the Discriminant | 二次方程与判别式
asily, use the quadratic formula with the equation written in standard form ax² + bx + c =
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