prove that ` 2(bc cos A +ca cos B +ab cos C)= a ^2+ b^2 +c ^2`

In any DeltaABC , prove that : a cos A + b cos B + c cos C = 2a sin B sin C

In any DeltaABC , prove that : a^2 +b^2 +c^2 = 2 (bc cos A + ca cos B + ab cos C) .

In any DeltaABC , 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 any DeltaABC, 2 [bc cos A + ca cos B+ ab cos C]=

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

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

If A + B + C = pi then prove that cos A + cos B + cos C = 1 + 4 sin(A/2) .sin(B/2).sin(C/2)

If A+B+C=180^0 , prove that : cos^2 (A/2) + cos^2 (B/2) - cos^2 (C/2) = 2cos (A/2) cos (B/2) sin (C/2)

Prove that bc cos^(2).(A)/(2) + ca cos^(2).(B)/(2) + ab cos^(2).(C)/(2) = s^(2)