📚 IGCSE Trigonometry: Complete Study Guide | IGCSE三角学：完整学习指南
Trigonometry is one of the most important topics in IGCSE Mathematics. It connects geometry with algebra and appears in both Paper 2 and Paper 4, often worth 15-20 marks in total across multiple questions. This guide covers everything you need to know, from right-angled triangle ratios to the sine rule, cosine rule, and trigonometric graphs.
三角学是IGCSE数学中最重要的主题之一。它将几何与代数紧密联系，在Paper 2和Paper 4中都会出现，通常在多道题目中合计占15-20分。本指南涵盖了您需要掌握的全部内容，从直角三角形三角比到正弦定理、余弦定理以及三角函数图像。
1. Right-Angled Triangle Trigonometry (SOH CAH TOA) | 直角三角形三角学（SOH CAH TOA）
For any right-angled triangle, we define three primary trigonometric ratios: sine (sin), cosine (cos), and tangent (tan). These ratios relate the angles of the triangle to the lengths of its sides. The hypotenuse is the longest side, always opposite the right angle. The opposite side is directly across from the reference angle θ, and the adjacent side is the side next to the angle θ that is not the hypotenuse.
对于任何直角三角形，我们定义三个基本三角比：正弦（sin）、
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