In triangle ABC: angle C is 900, BC = 2, AC = 4. Find cosB.

univerkov | May 21, 2021 | education

Determine, by the Pythagorean theorem, the length of the hypotenuse AB.

AB ^ 2 = AC ^ 2 + BC ^ 2 = 16 + 4 = 20.

AB = √20 = 2 * √5.

Then CosB = CB / AB = 2/2 * √5 = 1 / √5 = √5 / 5.

Answer: CosB = √5 / 5.

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