In an isosceles triangle ABC, AC = BC = 20, AB = 10. Find the cosine of the angle BАС.

univerkov | September 5, 2021 | education

Given:
AC = BC = 20
AB = 10

Find:
cos (BAC) -?

1) Draw the CH height to the base AB;
2) In an isosceles triangle, the height is also the median:
AH = BH = AB / 2 = 10/2 = 5;
3) Calculate the cosine of the angle BAC:
cos (BAC) = AH / AC = 5/20 = 0.25.

Answer: The cosine of the BAC angle is 0.25.

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