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

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 any Delta ABC, prove that :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 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

cos(A+B)*cos(A-B)= (a) sin^2A-cos^2B (b) cos^2A-sin^2B (c) sin^2A-sin^2B (d) cos^2A-cos^2B

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

In /_ABC 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 any Delta ABC, 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

If any triangle ABC, 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 /_ABC, prove that cos^(2)(2A)+cos^(2)(2B)+cos^(2)(2C)=1+2cos2A cos2B cos2C