In a right-angled triangle ABC, angle C = 90 degrees, Angle B = 60 degrees, AB = 15cm. Find BC
| August 5, 2021 | education
A rectangular triangle is a triangle in which one of the corners is straight, that is, it is equal to 90º.
Since, according to the condition of the problem, we know the value of the angle ∠B and the length of the hypotenuse AB, it is most convenient to use the cosine theorem to calculate BC, according to which, the cosine of an acute angle of a right-angled triangle is the ratio of the adjacent leg to the hypotenuse:
cos B = BC / AB.
Thus:
BC = AB cos B.
The cosine of 60º is 1/2 or 0.5.
BC = 15 0.5 = 7.5 cm.
Answer: the length of the BC leg is 7.5 cm.
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