In triangle ABC, angle C is 90 cosA = 4/5. Find cosB.

univerkov | May 1, 2021 | education

Let the length of the leg AC = 4 * X cm, then the length of the hypotenuse AB = 5 * X cm.

Then, by the Pythagorean theorem, BC ^ 2 = AB ^ 2 – AC ^ 2 = 25 * X ^ 2 – 16 * X ^ 2 = 9 * X ^ 2.

BC = 3 * X cm.

Then CosABC = BC / AB = 3 * X / 5 * X = 3/5.

Answer: The cosine of angle B is 3/5.

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