`a^(2) (cos^(2) B - cos^(2) C) + b^(2) (cos^(2) C - cos^(2) A) + c^(2) (cos^(2) A -cos^(2) B) = 0`.

In Delta ABC prove that a^2(cos^2B - cos^2C) + b^2(cos^2C - cos^2A) + c^2(cos^2A - cos^2B) = 0

In any triangle ABC, prove that following: (cos^(2)B-cos^(2)C)/(b+c)+(cos^(2)C-cos^(2)A)/(c+a)+(cos^(2)A-cos^(2)B)/(a+b)=0

a^2(cos^2B-cos^2C)+b^2(cos^2C-cos^2A)+c^2(cos^2A-cos^2B)=0 .

In any DeltaABC , prove that : (b^2 - c^2)/(cos B + cos C) + (c^2 - a^2)/(cos C + cos A) + (a^2 - b^2)/(cos A + cos B) = 0

In a quadrilateral if (sin (A + B)) / (2) (cos (AB)) / (2) + (sin (c + D)) / (2) + (sin (c + D)) / ( 2) (cos (cD)) / (2) = 2, then (cos A) / (2) (cos B) / (2) + (cos A) / (2) (cos c) / (2) + (cos A) / (2) (cos D) / (2) + (cos B) / (2) (cos C) / (2) + (cos B) / (2) (cos D) / (2) + (cos C) / (2) (cos D) / (2)

a cos ^(2) "" ( A) /(2) + b cos ^(2) "" ( B)/(2) = c cos ^(2) "" ( C) /(2) =

In /_\ABC prove that a^2(cos^2B-cos^2C)+b^2(cos^2C-cos^2A)+c^2(cos^2A-cos^2B) = 0

(vii) (b^(2) -c^(2)) cos 2A + (c^(2) -a^(2)) cos 2B + (a^(2) -b^(2)) cos 2C=0

(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

If A+ B + C = pi, then cos^(2) A + cos ^(2) B + cos ^(2) C is equal to : A) 1 - cos A cos B cos C B) 1 - 2 cos A cos B cos C C) 2 cos A cos B cos C D) 1 + cos A cos B cos C