In an acute-angled triangle ABC, the height of AH is 9√39, and the side AB is 60. Find cosB.

univerkov | September 28, 2021 | education

In a right-angled triangle ABH, we define the sine of the angle ABH.

SinABH = AH / AB = 9 * √39 / 60 = 3 * √39 / 20.

Then Cos2ABH = 1 – Sin2ABH = 1 – 351/400 = 49/400.

CosАВН = 7/20

Answer: The cosine of the angle ABC is 7/20.

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