In `Delta ABC if b+c:c+a:a+b=11:12:13`, then `cos A: cos B: cos C`=

In Delta ABC,a(b cos C-c cos B)=

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

In Delta ABC, cos A + cos (B-C)=

In a triangle ABC, a cos A+b cos B+ c cos C=

In Delta ABC, prove that :(c-b cos A)/(b-c cos A)=(cos B)/(cos C)

In Delta ABC , a( b cos C - c cos B) =