# Grade 9 Mathematics Module: The Law of Cosines and Its Applications

This Self-Learning Module (SLM) is prepared so that you, our dear learners, can continue your studies and learn while at home. Activities, questions, directions, exercises, and discussions are carefully stated for you to understand each lesson.

Each SLM is composed of different parts. Each part shall guide you step-by-step as you discover and understand the lesson prepared for you.

Pre-tests are provided to measure your prior knowledge on lessons in each SLM. This will tell you if you need to proceed on completing this module or if you need to ask your facilitator or your teacherâ€™s assistance for better understanding of the lesson. At the end of each module, you need to answer the post-test to self-check your learning. Answer keys are provided for each activity and test. We trust that you will be honest in using these.

Please use this module with care. Do not put unnecessary marks on any part of this SLM. Use a separate sheet of paper in answering the exercises and tests. And read the instructions carefully before performing each task.

In the last module you already learned how to solve an oblique triangle given the two angles and one side (SAA Case and ASA Case) or given two sides and an angle opposite a given side (SSA Case) using the Law of Sines. But not all oblique triangles can be solved using the Law of Sines. What if you are given two sides and an included angle (SAS case) or the three sides (SSS case)? Can you solve the oblique triangle using the Law of Sines? In this module you will learn how to solve oblique triangles using the Law of Cosines.

After going through with this module, you are expected to be able to illustrate law of cosines.

MATH9-Q4-MOD8

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