📚 CCEA Year 9 Maths: Quick Guide to Key Terms & Vocabulary | CCEA 九年级数学：核心术语速记指南
Mastering mathematical vocabulary is the first step to excelling in CCEA Year 9 Maths. This guide provides memorable explanations for key terms across Number, Algebra, Geometry, Statistics, and more, helping you to understand and retain essential concepts efficiently.
掌握数学词汇是在CCEA九年级数学中取得优异成绩的第一步。本指南为代数、几何、统计等领域的核心术语提供了易记的解释，帮助你高效理解和记住基本概念。
1. Number Types & Place Value | 数的类型与位值
An integer is any whole number that can be positive, negative, or zero. It does not include fractions or decimals. Remember 'integer' like 'intact' — whole and unbroken.
整数是任何正整数、负整数或零，不包括分数和小数。记忆：“整数”即“完整”的数，就像'intact'（完好无损）。
A prime number is a number greater than 1 that has exactly two factors: 1 and itself. For example, 7 is prime because only 1 and 7 divide evenly into it. Think of a 'prime cut' of meat — nothing extra, just the essential parts.
质数是大于1且只有两个因数（1和自身）的数。例如7是质数。联想“prime cut”（上等肉块），就是精华部分，没有多余的因数。
A composite number has more than two factors. For instance, 6 has factors 1, 2, 3, and 6. Composite comes from 'compose' — built from multiple parts, like a composite material.
合数有多于两个因数。例如6有因数1, 2, 3, 6。Composite源于“compose”（组成），是由多个部分构成的，如同复合材料。
Place value tells us the value of a digit based on its position in a number. In 5 432, the digit 5 is worth 5 thousands, 4 is worth 4 hundreds, 3 tens, and 2 ones. Use a place value chart to see this clearly.
位值表示数字中某一位数码基于其位置所代表的值。在5432中，数字5表示5个千，4表示4个百，3个十，2个一。可以用位值表清晰展示。
| Thousands (千位) | Hundreds (百位) | Tens (十位) | Ones (个位) |
| 5 | 4 | 3 | 2 |
Even integers end in 0, 2, 4, 6, or 8 and are divisible by 2. Odd integers end in 1, 3, 5, 7, or 9. 'Even' sounds like 'evenly shared', no remainder.
偶数以0、2、4、6、8结尾，能被2整除。奇数以1、3、5、7、9结尾。“Even”听上去像“平均分配”，没有余数。
2. Fractions, Decimals & Percentages | 分数、小数与百分数
The numerator is the top number of a fraction; it tells how many parts we have. The denominator is the bottom number; it tells how many equal parts the whole is divided into. A rhyme: 'Numerator above the line, denominator down below — that's the fraction show.'
分子是分数线上方的数，表示有几份。分母是线下方的数，表示整体被分成了几等份。顺口溜：“分子在上，分母在下，分数你好。”
= 2/4 = 4/8. To find equivalents, multiply or divide both parts by the same number. Think 'equal value in different forms'.
等值分数表示相同的量但使用不同的分子和分母，例如1/2 = 2/4 = 4/8。要得到等值分数，将分子分母同时乘以或除以相同的数。记成“不同形式、相同价值”。
A decimal uses a decimal point to separate whole numbers from parts of a whole. Each place after the point is tenths, hundredths, thousandths... Imagine a 'decimal detective' pointing out fragments.
小数用小数点分隔整数部分和小数部分。小数点后依次是十分位、百分位、千分位……想象一位“小数侦探”在指出碎片。
A percentage means 'out of 100'. The symbol % comes from the Italian 'per cento'. To convert a decimal to a percentage, multiply by 100: 0.75 × 100 = 75%. To go back, divide by 100.
百分数表示“每一百份中的几份”。符号%来自意大利语“per cento”。将小数转化为百分数，乘以100：0.75 × 100 = 75%。反之除以100。
Decimal → Percentage: 0.65 × 100 = 65%
3. Algebraic Expressions | 代数表达式
A variable is a symbol (often a letter) that represents an unknown number, e.g., x, y, n. Think of it as a 'variable container' that can hold different values depending on the problem.
变量是用字母表示未知数的符号，如x、y、n。可以想象成一个“可变容器”，能根据不同问题存放不同的值。
A coefficient is the number multiplied by the variable. In 7a, 7 is the coefficient. If no number appears, the coefficient is 1 (so m means 1m). 'Co-' means together, it works with the variable.
系数是与变量相乘的数字。在7a中，7是系数。如果没有数字，系数为1（m即1m）。‘Co-’表示共同，系数与变量共同出现。
A term is a single number, variable, or product of numbers and variables. Like terms have the exact same variable part, e.g., 5p and -2p are like; 3y² and 4y are unlike. Combine like terms by adding/subtracting coefficients.
项是单独的数、变量或数与变量的乘积。同类项有完全相同的变量部分，如5p和-2p；3y²和4y不是同类项。合并同类项可通过系数相加或相减。
Simplify: 4x + 3y - 2x + y = (4x - 2x) + (3y + y) = 2x + 4y
An expression is a collection of terms combined by operators, without an equals sign. It's like a phrase in mathematics, not a complete sentence.
表达式是由项通过运算符号组合而成，没有等号。它就像数学里的“短语”，不是完整的“句子”。
4. Equations & Inequalities | 方程与不等式
). Solving an equation means finding the value(s) of the variable that make the statement true. Think of a balanced scale: both sides must have equal weight.
方程用等号（=）表明两个表达式相等。解方程就是找到使等式成立的变量值。想象一个平衡的天平：两边重量必须相等。
her side to keep the equation balanced. For x + 5 = 12, subtract 5 from both sides: x = 7.
平衡法：对等式一边进行任何运算，另一边必须进行完全相同的运算以保持平衡。例如x + 5 = 12，两边同时减5得x = 7。
x + 5 = 12 → x = 12 − 5 → x = 7
less than), > (greater than), ≤ (less than or equal to), ≥ (greater than or equal to). The 'open' side always faces the larger number, like a hungry mouth: 3 < 7.
不等式使用符号比较两个值：<（小于），>（大于），≤（小于等于），≥（大于等于）。开口始终朝向较大的数，就像一张饥饿的嘴巴：3 < 7。
you must reverse the inequality sign. Example: -2x < 6 → divided by -2 flips sign: x > -3.
解不等式与解方程类似，但如果乘以或除以负数，必须反转不等号。如-2x < 6，两边除以-2得x > -3。
5. Angles & Lines | 角与线
An acute angle measures less than 90°. Remember: 'a cute' small angle — cute things are often small.
锐角小于90度。记忆：'acute'听起来像'a cute'，可爱的角小小的。
An obtuse angle is between 90° and 180° (exclusive). Obtuse sounds like 'obese' — wide and heavy. An angle between 90° and 180° is wide.
钝角在90°到180°之间（不含端点）。Obtuse听起来像“obese”（肥胖），又宽又大。
A reflex angle is greater than 180° but less than 360°. Reflex suggests a bending backward, like a reflex action. It goes the 'long way round'.
优角大于180°且小于360°。Reflex意为反射，像手臂向后弯曲，走了“长路”。
A right angle is exactly 90° and is often marked with a small square. Think of the upright 'right' corner of a picture frame.
直角正好是90度，通常用一个小方格标记。想象画框那个竖直的“直角”。
Parallel lines are always the same distance apart and never meet. The symbol is //. The word 'parallel' contains two l's like two rails.
平行线始终保持相同距离，永不相交，符号是//。单词“parallel”中有两个l，像两条铁轨。
Perpendicular lines intersect at a right angle (90°). Symbol: ⟂. 'Perpendicular' contains 'pend', like pendulum hanging exactly vertically.
垂线相交成直角（90°），符号⟂。'Perpendicular'中含有'pend'，像钟摆垂直悬挂。
6. 2D Shapes and Symmetry | 二维图形与对称
A polygon is a closed 2D shape bounded by straight line segments. Triangles (3 sides), quadrilaterals (4), pentagons (5), hexagons (6)... 'Poly' means many, 'gon' means angle.
多边形是由直线段围成的封闭二维图形。三角形（3边）、四边形（4边）、五边形（5边）、六边形（6边）……“Poly”意为多，“gon”指角。
A regular polygon has all sides equal and all angles equal, like
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