In ` A B C ,` prove that `cos e c A/2+cos e c B/2+cos e c C/2geq6.`

If A + B + C = pi , prove that cos A cosec B cosec C + cos B cosec C cosec A + cos C cosec A cosec B = 2 .

In a /_ABC prove that cos2A+cos2B+cos2C=-1-4cos A cos B cos C

If A +B+C = 180^circ , prove that cos A/2+ cos B/2 +cos C/2 = 4cos (pi-A)/4 * cos(pi-B)/4 cos(pi-C)/4

If A+B+C=pi , prove that cos 2A +cos 2B +cos 2C=-1-4cos A cos Bcos C.

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)

In triangle ABC , prove that (1) a=b cos C+c cos B (2) b=a cos C+c cos A .

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)

If A + B + C + D = 2pi , prove that: cos A + cos B + cos C + cos D =-4"cos"(A+B)/(2)"cos"(A+C)/(2)"cos"(A+D)/(2)

If a,b and c be in A.P. prove that cos A cot((A)/(2)),cos B cot((B)/(2)), and cos C cot((C)/(2)) are in A.P.

For any triangle ABC,prove that a cos A+b cos B+c cos C=2a sin B sin C