ACT Preparation / Unit 14 ACT 1330 short lesson, about 20 seconds
The Laws of Sines and Cosines
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The idea
In any triangle, a/sin A = b/sin B = c/sin C, the law of sines; and c² = a² + b² − 2ab cos C, the law of cosines.
In practice
Sides 5 and 8 around 60°: c² = 25 + 64 − 40 = 49, so c = 7.
Where people slip
At C = 90°, the law of cosines becomes the Pythagorean theorem.
Your place on the trail
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