(vi) `a cos B cos C + b cos C cosA + c cosA cos B=(abc)/(4R^(2))`

(xiv) a cos A + b cos B + c cos C = (abc)/(2R^(2))

cos^2 A + cos^2 B +cos^2 C=1+2cosA cosB cosC .

(iii) a cosA + b cos B + c cos C = 4R sin A sin B sinC

In any Delta ABC, prove that : (cos A)/(b cos C+c cos B)+(cos B)/(c cos A+a cos C)+(cos C)/(c cos B+b cos A)=(a^(2)+b^(2)+c^(2))/(2abc)

In any Delta ABC, prove that: (cos A)/(b cos C+c cos B)+(cos B)/(c cos A+a cos C)+(cos C)/(a cos B+b cos A)=(a^(2)+b^(2)+c^(2))/(2abc)

if A + B +C= pi/2 ,prove that cos(A - B - C)+ cos (B-C- A) + cos (C- A - B)= 4 cos A cos B cos C

With usual notations,in triangle ABC,a cos(B-C)+b cos(C-A)+c cos(A-B) is equal to (a)(abc)/(R^(2)) (b) (abc)/(4R^(2)) (c) (4abc)/(R^(2)) (d) (abc)/(2R^(2))

(v) (b^(2)-c^(2))/(cos B + cos C) + (c^(2)-a^(2))/( cos C + cosA) + (a^(2)-b^(2))/(cos A + cos B)=0