Year 9 Cambridge Maths: Formula & Theorem Quick Reference Handbook | 九年级剑桥数学：公式定理速查手册

📚 Year 9 Cambridge Maths: Formula & Theorem Quick Reference Handbook | 九年级剑桥数学：公式定理速查手册

This quick reference handbook summarises the essential formulas, theorems, and key concepts for Year 9 Cambridge Mathematics. It is designed to help you review and consolidate the topics covered in the Cambridge Lower Secondary or IGCSE foundation course. Each section presents the core ideas in a clear, bilingual format for easy memorisation and application.

本速查手册总结了九年级剑桥数学的基本公式、定理和核心概念，旨在帮助学生复习和巩固剑桥初中或 IGCSE 基础课程中的内容。每个小节都以清晰的双语形式呈现核心要点，方便记忆和运用。

1. Number and Arithmetic | 数与算术

Fractions with a common denominator: a/d + b/d = (a + b)/d. For different denominators, find the LCD: a/b + c/d = (ad + bc)/bd.

同分母分数相加：a/d + b/d = (a + b)/d。异分母分数相加，先求最小公分母：a/b + c/d = (ad + bc)/bd。

Multiplication and division of fractions: a/b × c/d = ac/bd; a/b ÷ c/d = a/b × d/c = ad/bc.

分数乘除法：a/b × c/d = ac/bd；a/b ÷ c/d = a/b × d/c = ad/bc。

Converting between fractions, decimals, and percentages: e.g., 0.25 = 1/4 = 25%. Multiply by 100 to change a decimal to a percentage.

分数、小数和百分数互化：如 0.25 = 1/4 = 25%。将小数乘以100得到百分数。

Percentage increase or decrease: New value = original value × (1 ± r/100), where r is the percentage. Alternatively, New = original × (1 ± r) if r is in decimal form.

百分比增减：新值 = 原值 × (1 ± r/100)，其中 r 是百分数。或新值 =

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