A right-angled triangle is a triangle in which one of the angles is 90 °.
To calculate the length of the side BC, we use the cosine theorem. 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;
cos 60º = 1/2;
ВС = AB ∙ cos B;
BC = 15 ∙ 1/2 = 15/2 = 7.5 cm.
Answer: The length of the BC side is 7.5 cm.
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