In triangle ABC, angle a is 90 AC = 15 cm; cosine of angle B is 12/13, find the length of the side BC.

univerkov | May 4, 2021 | education

Since CosABC = 12/13, AB = 12 * X, BC = 13 * X cm.

Then, by the Pythagorean theorem, BC ^ 2 = AB ^ 2 + AC ^ 2.

169 * X ^ 2 = 144 * X ^ 2 + 225.

25 * X ^ 2 = 225.

X ^ 2 = 9.

X = 3.

Then BC = 13 * 3 = 39 cm.

Answer: The length of the BC side is 39 cm.

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