If `b+c:c+a:a + b = 11:12:13`, then `cos A : cos B : cos C=`

(a + b + c) (cos A + cos B + cos C)

With usual notation , if in triangle ABC, (b + c)/11 = (c + a)/12 = (a + b)/13 , then cos A : cos B : cos C =

With usual notations, if in a triangle ABC (b+c)/(11) = (c+a)/(12) = (a+b)/(13) , then cos A : cos B : cos C is :

With usual notations, if in a triangle ABC (b+c)/(11) = (c+a)/(12) = (a+b)/(13) , then cos A : cos B : cos C is :

If cos A+ cos B + cos C=0 , prove that cos 3A + cos 3B + cos 3C = 12 cos A cos B cos C

If A+B+C=pi , then cos B+cos C=