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Cosine Law

Mathematics · Class 10

Two sides and included angle, or three sides. Finding an angle: cos C = a²+b²-c²2ab. Do not use cosine law when you only have AAS and no SAS/SSS.

included angle or SSS
a/sin A = b/sin B
c² = a²+b²-2ab cos C
keep the ideas separate
Cosine Law: Two sides and included angle, or three sides. Finding an angle: cos C = a²+b²-c²2ab. Do not
WHAT — COSINE LAW: Two sides and included angle, or three sides. Finding an angle: cos C = a²+b²-c²2ab. Do not
HOW — Use the idea: Identify what is given, select this topic's rule or evidence, apply it one step at a time, and check
CORE UNDERSTANDING: Two sides and included angle, or three sides. Finding an angle: cos C = a²+b²-c²2ab. Do not

Right triangle — Cosine Law — original sketch for this lesson (not copied from a textbook).